The Technology of Sliding Timing Window (TSTW) can define the starting and ending time of GPS data involved in data processing. Using TSTW, the latest observations can be added into the real time data processing with more actual results. Using a timing window with fixed widths, the accuracy of ambiguity resolution can be guaranteed with the least occupation of computer resources. Using TSTW and getting observations from 6 IGS (International GNSS Service) stations in China in 2008, the parameters for the troposphere at these 6 stations are calculated. Using the daily Zenith Total Delay (ZTD) of the stations that posted on the website of CODE as normal values, the standard deviations are calculated, respectively, and the influences on the accuracy and the real time properties of ZTD solution by timing windows with different widths are analyzed. The operational system of “Ground based GPS Real time Water Vapor Retrieval” using TSTW can gain the parameters in the troposphere with high accuracy and meanwhile meet the real time demands of operation. The best timing window width is about 8 hours.