Abstract: By analyzing a lot of location measurement data of GPS, the conclusion that GPS fixed point coordinate is constitute of location excursion and normal school is drawn. In order to separate location excursion data from normal school data, normal school elimination measure and the center point calculation rule are used, and a measure of calculating the fixed point error radius in a certainty clique value is presented. Aimed at the characteristic of bigger single point location error, a new measuring method using two points relative location measurement to reduce location measurement error was put forward. The test result indicated that when clique value is 0.7, the single location error is over 10 meters, however when two points relative location measuring method is used, its location error is about 1.2 meter, improving its measuring precision greatly. The two relative location measurement method can also be used to measure ground, orientation and layout.