diff --git a/crontab.go b/crontab.go
index 7d7a424..e6d3946 100644
--- a/crontab.go
+++ b/crontab.go
@@ -185,12 +185,14 @@ func (cron *Crontab) FromString(crontab string) error {
 		// "f1-2|5-10x5,f1|10m,10-15,f1"
 
 		cron.lastStatus = true
-		cron.isCalculated = false
+		cron.isCalculated = true
+		cron.nextTime = time.Now()
+
 		cron.interval = clinked.NewCircularLinked()
 		var intervalList []interface{}
 		intervalList = parseIntervalString(matches[0])
 		cron.interval.Append(intervalList...)
-		cron.TimeUp()
+
 	case 5:
 		cron.min = createTimePointer(matches[0], 0, 59, true)
 		cron.hour = createTimePointer(matches[1], 0, 23, true)
@@ -328,7 +330,7 @@ func (cron *Crontab) intervalCalculateNextTime(now time.Time) {
 
 func (cron *Crontab) intervalTimeUp() bool {
 
-	if cron.isCalculated != false {
+	if cron.isCalculated { // 需要调用nexttime()才能正常正常计算下次的时间
 		now := time.Now()
 		if now.Unix() >= cron.nextTime.Unix() {
 			cron.isCalculated = false