What's Horizontal align feature of Label in CC 3.6?

How it must work actually? it works only if ‘Overflow’ enabled, why?

You can see how it works after you warp your text.
动画2

Well, is there only way to use Overflow , if i need this feature only for single line? i think it’s quite weird behavior if compare to Unity

Yes, if you need this feature only for single line, you can use Overflow, it will limit the width.