Thanks a lot!
Finally it shows up.
It's my mistake to input all the code at once.
Should be run step by step.

first open Terminal.app
then:

mkdir -p ~/Documents/Arduino/hardware/espressif
cd /Documents/Arduino/hardware/espressif
git clone https://github.com/espressif/arduino-esp32.git esp32
cd esp32/tools
python get.py

then open/restart Arduino IDE

Thanks for your help!
I do it several times, but IDE ...

I try follow github to add ESP32 on mac,but still not show in Arduino IDE (1.6.12) .
Please show me step by step.Thanks!