lag on local server

I create a local server and a fresh install of mc, then Im noticing a server like lag so as when I hit an animal or monster ,it will float about 0.5-2 seconds. it just only makes mobs lag , if i install the forge ,the situation of lag will more serious.anyway,the object is normal,if i destory a dirt , i will get the element immediately
i think Its not fps lag , Ive tested in singleplayer model .