Thanks LeandroSouza. I tried this method last time, but it could not work. I will share the troubleshooting methods that I have tried and eventually, how was the problems solved in July this year. 

This problem had been started since October 2014. We had done analysis on the WinCC diagnose files, checked on all the logs especially SIMATIC_S7_Protocol_Suite_01.LOG. We found that was a lot of error code such as 0x0000 7002, 0xFFDF 01FF, 0xFFDF 4022, 0xFFDF 01FF, and etc. We traced the error code, increase s7 protocol Named connection life beat monitoring time, upgrade our cpu firmware to the latest one, change our network architecture from domain to workgroup, but the problem still could not be solved.

Lastly, I had recompile the os, change the s7 protocol from named connection to industrial Ethernet. The connection problem of OS and PLC was solved.