Gladly to annouce that now it is a solved problem.
Originally I always got US time (GMT -5:00 format time ) though I am located in Shanghai, China (GMT +8:00 time ), and the timezone setting in my Windows OS has always been GMT+8:00, which is correct for my timezone.
last night I got a hint from a PM from Dav of IB, and made a test to change my Windows timezone setting to another one( GMT +5:00), and restart TWS. Amazingly now the TWS shows the local time of GMT +5:00 . So I closed TWS, and changed Windows timezone setting back to GMT +8:00 and restarted TWS, everything is OK now, TWS now shows my local time correctly in the lower right corner.
I think when TWS does not show local time correctly, you can repeat the above operation, change the Windows timezone setting twice and the problem will be solved.
Many thanks to Dav. I can view TWS execution list (whose time format is in my local time now ) during the trading session much more efficiently now.