diff --git a/pkg/scriptcat/utils.go b/pkg/scriptcat/utils.go
index 1f31f0c..5c2a362 100644
--- a/pkg/scriptcat/utils.go
+++ b/pkg/scriptcat/utils.go
@@ -36,11 +36,24 @@ func ConvCron(cron string) (string, error) {
 	}
 	for i, v := range unit {
 		if v == "once" {
+			// once -> *
 			unit[i] = "*"
-			i -= 1
-			for ; i >= 0; i-- {
-				if unit[i] == "*" {
-					unit[i] = "0"
+			for j := i - 1; j >= 0; j-- {
+				if unit[j] == "*" {
+					unit[j] = "0"
+				}
+			}
+			break
+		} else if strings.HasPrefix(v, "once(") && strings.HasSuffix(v, ")") {
+			// once(expr) -> expr
+			expr := v[len("once(") : len(v)-1]
+			if expr == "" {
+				return "", errors.New("once() expression cannot be empty: " + v)
+			}
+			unit[i] = expr
+			for j := i - 1; j >= 0; j-- {
+				if unit[j] == "*" {
+					unit[j] = "0"
 				}
 			}
 			break