diff --git a/package.json b/package.json
index 58a63ba..89eaa01 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@lay2/pw-core",
-  "version": "0.3.20-beta.2",
+  "version": "0.3.20-beta.3",
   "description": "the javascript sdk of pw-sdk",
   "main": "build/main/index.js",
   "typings": "build/main/index.d.ts",
@@ -109,4 +109,4 @@
       "**/*.spec.js"
     ]
   }
-}
+}
\ No newline at end of file
diff --git a/src/models/amount.spec.ts b/src/models/amount.spec.ts
index 25420e7..c766bf4 100644
--- a/src/models/amount.spec.ts
+++ b/src/models/amount.spec.ts
@@ -3,6 +3,7 @@ import PWCore, { ChainID } from '../core';
 import { DummyCollector } from '../collectors/dummy-collector';
 import { Amount, AmountUnit } from '.';
 import { DummyProvider } from '../providers/dummy-provider';
+import JSBI from 'jsbi';
 
 test.before(async () => {
   await new PWCore('https://aggron.ckb.dev').init(
@@ -127,4 +128,17 @@ test('to hex string', (t) => {
   t.is(shannonFull.toHexString(), '0xe94c0e8734');
 });
 
-test.todo('random decimal test');
+// tests for random decimals
+
+const d0 = new Amount('10', 0);
+const d1 = new Amount('1', 1);
+const d2 = new Amount('0.1', 2);
+const p = new Amount('0.00361', AmountUnit.ckb);
+
+test.only('to BigInt', (t) => {
+  t.is(d0.toBigInt().toString(), JSBI.BigInt(10).toString());
+  t.is(d1.toBigInt().toString(), JSBI.BigInt(10).toString());
+  t.is(d2.toBigInt().toString(), JSBI.BigInt(10).toString());
+  t.is(p.toString(), '0.00361');
+  t.is(p.toString(AmountUnit.shannon), '361000');
+});
diff --git a/src/models/amount.ts b/src/models/amount.ts
index a00a57b..8496b7b 100644
--- a/src/models/amount.ts
+++ b/src/models/amount.ts
@@ -2,10 +2,9 @@ import JSBI from 'jsbi';
 import {
   toBigUInt128LE,
   readBigUInt128LE,
-  rationalNumberToBnString,
   bnStringToRationalNumber,
+  rationalNumberToBnString,
 } from '../utils';
-import { HexStringToBigInt } from 'ckb-js-toolkit';
 
 export enum AmountUnit {
   shannon,
@@ -36,7 +35,7 @@ export class Amount {
   mul(val: Amount): Amount {
     const res = JSBI.divide(
       JSBI.multiply(this.toBigInt(), val.toBigInt()),
-      JSBI.BigInt(10 ** (val.decimal + this.decimal))
+      JSBI.BigInt(10 ** (val.decimals + this.decimals))
     ).toString();
     return new Amount(res, AmountUnit.shannon);
   }
@@ -62,52 +61,33 @@ export class Amount {
   }
 
   private amount: string;
-  private decimal: number;
-
-  constructor(amount: string, unit?: AmountUnit);
-  constructor(amount: string, decimal: number = 8) {
-    if (Number.isNaN(amount)) {
-      throw new Error(`Amount ${amount} is not a valid number`);
-    }
-    amount = `${amount}`;
+  private decimals: number;
 
-    if (!Number.isInteger(decimal) || decimal < 0) {
-      throw new Error(`Decimal ${decimal} must be a natural number`);
+  constructor(amount: string, decimals: number | AmountUnit = AmountUnit.ckb) {
+    if (!Number.isInteger(decimals) || decimals < 0) {
+      throw new Error(`decimals ${decimals} must be a natural number`);
     }
-    this.decimal = decimal;
+    this.decimals = decimals;
 
-    if (amount.startsWith('0x')) {
-      amount = HexStringToBigInt(amount).toString();
-    }
-
-    if (decimal === AmountUnit.shannon) {
-      try {
-        amount = amount.match(/^0*(\d*)$/)[1];
-        if (amount === '') {
-          amount = '0';
-        }
-      } catch (e) {
-        throw new Error(`Amount ${amount} is invalid`);
-      }
+    if (Number.isNaN(amount)) {
+      throw new Error(`amount ${amount} must be a valid number`);
     }
-    this.amount = amount;
-    this.decimal = decimal;
+    this.amount = rationalNumberToBnString(amount, decimals);
   }
+
   toString(
-    decimal = AmountUnit.ckb as number,
+    decimals: number | AmountUnit = AmountUnit.ckb,
     options?: FormatOptions
   ): string {
     return bnStringToRationalNumber(
       this.toBigInt().toString(),
-      decimal,
+      decimals,
       options
     );
   }
 
-  toBigInt(decimal?: number) {
-    return JSBI.BigInt(
-      rationalNumberToBnString(this.amount, decimal || this.decimal)
-    );
+  toBigInt() {
+    return JSBI.BigInt(this.amount);
   }
 
   toHexString() {
diff --git a/src/models/sudt.ts b/src/models/sudt.ts
index 53dd13b..243ed54 100644
--- a/src/models/sudt.ts
+++ b/src/models/sudt.ts
@@ -3,7 +3,7 @@ import PWCore from '../core';
 
 export interface SudtInfo {
   symbol: string;
-  decimal: number;
+  decimals: number;
   name: string;
 }
 export class SUDT {
diff --git a/src/utils.ts b/src/utils.ts
index 29b8597..076bc95 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -16,11 +16,11 @@ export const ckbToShannon = (ckbAmount: string): string =>
 
 export const bnStringToRationalNumber = (
   bn: string,
-  decimal: number,
+  decimals: number,
   options: FormatOptions
 ) => {
-  if (!Number.isInteger(decimal) || decimal < 0) {
-    throw new Error("value of 'decimal' must be a positive integer");
+  if (!Number.isInteger(decimals) || decimals < 0) {
+    throw new Error("value of 'decimals' must be a natural integer");
   }
 
   const n = new Decimal(bn);
@@ -30,8 +30,8 @@ export const bnStringToRationalNumber = (
 
   let int = bn;
   let dec = '';
-  if (decimal > 0) {
-    const intLen = bn.length - decimal;
+  if (decimals > 0) {
+    const intLen = bn.length - decimals;
     int = intLen > 0 ? bn.substr(0, intLen) : '0';
     dec = intLen > 0 ? bn.slice(intLen) : `${'0'.repeat(-intLen)}${bn}`;
     dec = new Decimal(`0.${dec}`).toFixed().slice(2);
@@ -41,11 +41,12 @@ export const bnStringToRationalNumber = (
     if (options.fixed) {
       if (
         !Number.isInteger(options.fixed) ||
-        options.fixed < 1 ||
-        options.fixed > decimal
+        options.fixed < 1
+        // || options.fixed > decimals
       ) {
         throw new Error(
-          `value of \'fixed\' must be a positive integer and not bigger than decimal value ${decimal}`
+          // `value of \'fixed\' must be a positive integer and not bigger than decimals value ${decimals}`
+          `value of \'fixed\' must be a positive integer`
         );
       }
       const res = new Decimal(`0.${dec}`).toFixed(options.fixed).split('.');
@@ -53,8 +54,8 @@ export const bnStringToRationalNumber = (
       if (res[0] === '1') {
         int = JSBI.add(JSBI.BigInt(int), JSBI.BigInt(1)).toString();
       }
-    } else if (options.pad && dec.length < decimal) {
-      dec = `${dec}${'0'.repeat(decimal - dec.length)}`;
+    } else if (options.pad && dec.length < decimals) {
+      dec = `${dec}${'0'.repeat(decimals - dec.length)}`;
     }
     if (options.commify) {
       int = int.replace(/\B(?=(\d{3})+(?!\d))/g, ',');
@@ -75,20 +76,24 @@ export const bnStringToRationalNumber = (
   return int;
 };
 
-export const rationalNumberToBnString = (rational: string, decimal: number) => {
-  if (!Number.isInteger(decimal) || decimal < 0) {
-    throw new Error("value of 'decimal' must be a positive integer");
+export const rationalNumberToBnString = (
+  rational: string,
+  decimals: number
+) => {
+  if (!Number.isInteger(decimals) || decimals < 0) {
+    throw new Error("value of 'decimals' must be a natural integer");
   }
-  if (decimal === 0) return rational;
+  if (decimals === 0) return rational;
 
+  if (rational === '0x') rational = '0';
   const r = new Decimal(rational);
-  if (r.dp() > decimal) {
+  if (r.dp() > decimals) {
     throw new Error(
-      `Decimal ${decimal} is smaller than the digits number of ${rational}`
+      `decimals ${decimals} is smaller than the digits number of ${rational}`
     );
   }
 
-  return `${rational.split('.').join('')}${'0'.repeat(decimal - r.dp())}`;
+  return `${rational.split('.').join('')}${'0'.repeat(decimals - r.dp())}`;
 };
 
 // from @lumos/helper