I have one Pro Micro - 5V/16MHz[DEV-12640].(https://www.sparkfun.com/products/12640)
I’m new to arduino. I’ve been having a problem lately.
When the pro micro is powered by usb, the measured voltage of the Vcc pin is 6.8v. 
I know the normal vcc pin is 5v.
So, why is that? Is the pro micro broken? What should I do?
I would appreciate it if you could help me. Thank you!
(My English is a little poor, please forgive me.)
Something is wrong with your usb power source. Vcc connects directly to usb power, it will always be whatever voltage the usb power source is.
Firstly, thanks for your reply.I use the computer usb power source, and all my power source ports can normally power the mouse and keyboard (5V). So I don’t think it’s my usb power source, it’s the pro micro.
Something is wrong with how you are measuring the voltage. The Pro Micro has no mechanism to increase the supply voltage.
I’ve had multi meters give strange readings before when it’s batteries are low. Try a fresh battery in your meter.