Hi Xiu Yan Xu,

There are a lot of tutorials / information about this over Internet. You can look here:

https://www.youtube.com/watch?v=aQhiBlzKiRg

https://forums.autodesk.com/t5/autocad-forum/dimensioning-a-2d-isometric-drawing/td-p/5813190

https://www.neit.edu/blog/index.php/2015/09/autocad-placing-your-dimensions-and-text-on-the-right-an...

https://www.cadforum.cz/cadforum_en/isometric-dimensions-in-a-2d-drawing-tip7931

The information is about AutoCAD for Windows, but general concept is the same in AutoCAD for Mac.