Abstract: To study the relationship of accuracy of DGPS(differential global positioning system) vs. differential distances betweenstations, and vs. the differential pseudorange correction ages by analysis andexperiment. The results show that when differential distance between stations is less than 200 km and the differential pseudorange correction age is less than5s, the influence of various space correlated error and SA(selective availability) on DGPS accuracy is very small so that it can be ignored in ordinary situation,thus the resulting positioning errors are mainly concluded by receiver noise and multipath effect. While the time differential method introduced using the data of one GPS receiver,can effectively correct various error elements and improve the positioning accuracy without the need of setting a differential base station.

Key words: differential global positioning system, differential pseudorange correction age, selective availability