diff --git a/cmd/fetch.go b/cmd/fetch.go
index 09d5d8af20..12209aa182 100644
--- a/cmd/fetch.go
+++ b/cmd/fetch.go
@@ -4,8 +4,8 @@ import (
 	cmds "github.com/ipfs/go-ipfs-cmds"
 	"github.com/pkg/errors"
 
+	"github.com/docker/go-units"
 	paramfetch "github.com/filecoin-project/go-paramfetch"
-
 	"github.com/filecoin-project/venus/fixtures/assets"
 )
 
@@ -14,11 +14,11 @@ var fetchCmd = &cmds.Command{
 		Tagline: "fetch paramsters",
 	},
 	Options: []cmds.Option{
-		cmds.Uint64Option(Size, "size to fetch"),
+		cmds.StringOption(Size, "size to fetch, eg. 2Kib,512Mib,32Gib,64Gib"),
 	},
 	Run: func(req *cmds.Request, re cmds.ResponseEmitter, env cmds.Environment) error {
 		// highest precedence is cmd line flag.
-		if size, ok := req.Options[Size].(uint64); ok {
+		if sizeStr, ok := req.Options[Size].(string); ok {
 			ps, err := assets.GetProofParams()
 			if err != nil {
 				return err
@@ -29,7 +29,12 @@ var fetchCmd = &cmds.Command{
 				return err
 			}
 
-			if err := paramfetch.GetParams(req.Context, ps, srs, size); err != nil {
+			size, err := units.RAMInBytes(sizeStr)
+			if err != nil {
+				return err
+			}
+
+			if err := paramfetch.GetParams(req.Context, ps, srs, uint64(size)); err != nil {
 				return errors.Wrapf(err, "fetching proof parameters: %v", err)
 			}
 			return nil