Finally, I found the source - a service named "QQPCMgr RTP Service" running on my office computer, it's the real time protection service of "QQ PC Manager".
By disabling it, the time of the script in the question falls back to:
real 0m0.943s user 0m0.105s sys 0m0.231s
I have told the developers of QQPCMgr about this, hope they will find the reason.
This still much slower than Linux, but gets the same "real time" of other cygwin computers.
Thank you all!