1. Check the mac Apple icon, point [About This Mac]
2. Point [storage] 
When you put the mouse over roads, will each occupy much space.
3. Check the space.
4. System accounted for 69.74G
5. What is the system directory it?
Find system directory.
6. Review the space and the name of each directory.
7. Check out this sum, less than the sum of the foregoing. Explain some did not compute.
8. back to the terminal.
9. Enter command.
~ CD / Library
du command -sh *
You can list each directory size.
And then go on to find layers. To see what these files do, there is no need to stay.
Finally, I find, / Users / mac / Library / Android / sdk / system-images accounted for 36G.
This is a simulator, you can stay one or not stay. I left one.
Here vacate 34G.
This is the method used commands.
Above, with a view on this machine, but also to find a large space-directory. Then, back to the terminal, use the command find.
In the end I Mysql directory, find 6G.
Although many online article directory list, but the actual situation of each person will be different. So they should find their own.
If this issue, do not understand, you can add QQ group: PHP Q & A group. We will try to answer for you.