Abstract: In this paper,the impact of the origin positioning deviation on precision of GPS baseline is discussed theoretically,simulated calculation of the GPS raw data is made and the result fits well with that calculated theoretically.The following conclusions could be drawn:the origin positioning deviation does not affect the internal accuracy but makes a systematic error that varies with the origin positioning deviation and tyB m(B m is a mean latitude of the baseline)to the result of baseline.Finally,suggestions are made as to how to get a more accurate WGS84 coordinates when carrying on DGPS(Differential GPS)precise surveying.