Abstract: In this paper,the effects of height difference and the horizontal change of troposphere on the accuracy of GPS surveying is discussed at first.And then GPS observation data collected in several years from Hong Kong Continuously Reference Station Network is used to model the precise tropospheric delay.This model is based on estimated zenith tropospheric delay of all the stations using the Bernese GPS software.The input parameters of the model are day of year and location of the station.The testing results show that the tropspheric delay error can be reduce about 2 to 3 times compared to Saastamoinen model with standard meteorological parameters,and the effect is more remarkable when the height difference of two stations is large.