It was first time using GIMP, the function I need was pen pressure!
I tried to changed the setting on Tool Options panel but it seems not working.
without pen pressure, GIMP will be useless!
I took a quick look the tutorial but there has nothing I need.
Finally, I found the Input Devices in Edit menu.
Select "WACOM Tablet Pressure Stylus" and change the "Mode" to Screen.
change the Pressure Curve if you need.
now you should get the pen pressure!
選擇 "WACOM Tablet Pressure Stylus" 將"mode"改成Screen就可以了