diff --git a/cmd/pulls/merge.go b/cmd/pulls/merge.go
index 3213db3..cf127dc 100644
--- a/cmd/pulls/merge.go
+++ b/cmd/pulls/merge.go
@@ -44,13 +44,27 @@ var CmdPullsMerge = cli.Command{
 		ctx := context.InitCommand(cmd)
 		ctx.Ensure(context.CtxRequirement{RemoteRepo: true})
 
-		if ctx.Args().Len() != 1 {
-			return fmt.Errorf("Must specify a PR index")
-		}
+		var idx int64
+		var err error
+		if ctx.Args().Len() == 1 {
+			idx, err = utils.ArgToIndex(ctx.Args().First())
+			if err != nil {
+				return err
+			}
+		} else {
+			if ctx.LocalRepo == nil {
+				return fmt.Errorf("Must specify a PR index")
+			}
 
-		idx, err := utils.ArgToIndex(ctx.Args().First())
-		if err != nil {
-			return err
+			branch, _, err := ctx.LocalRepo.TeaGetCurrentBranchNameAndSHA()
+			if err != nil {
+				return err
+			}
+
+			idx, err = GetPullIndexByBranch(ctx, branch)
+			if err != nil {
+				return err
+			}
 		}
 
 		success, _, err := ctx.Login.Client().MergePullRequest(ctx.Owner, ctx.Repo, idx, gitea.MergePullRequestOption{
@@ -68,3 +82,19 @@ var CmdPullsMerge = cli.Command{
 		return nil
 	},
 }
+
+func GetPullIndexByBranch(ctx *context.TeaContext, branch string) (int64, error) {
+	prs, _, err := ctx.Login.Client().ListRepoPullRequests(ctx.Owner, ctx.Repo, gitea.ListPullRequestsOptions{
+		State: gitea.StateOpen,
+	})
+	if err != nil {
+		return 0, err
+	}
+
+	for _, pr := range prs {
+		if pr.Head.Ref == branch {
+			return pr.Index, nil
+		}
+	}
+	return 0, fmt.Errorf("No open PR for branch %s", branch)
+}