Abstract：There are weather condition differences in different location in small areas, as a result，the tropospheric delay can not be completely eliminated with the usually used double difference technology. In order to analyze the residual tropospheric delay effect which caused by the different weather condition between the ends of the baseline, several tests with baselines of different length were carried out by using the data from Hong Kong CORS. The followings conclusions can be drawn from these test results.1) When the baseline is more than 15 kilometers, the residual tropospheric delay is the main error sources affecting the accuracy of GPS height measurement, and the longer the baseline length is, the bigger the error of the residual tropospheric delay is. 2)When the baseline length is close to or over 30 kilometers, baseline solution often fails because of the lange residual tropospheric delay.3)The tropospheric delay in horizontal direction is more diversed in the humid and hot weather conditions, and the accuracy of the GPS height measurement decreases more.
