The methods of relative positioning,software and instruments etc.on GPS were briefly introduced, and the advantages and disadvantages on GPS position in the loess hilly area were discussed in detail on the basis of the field experiences on GPS position and an analyses on survey data in Ansai county,Shaanxi province of China.The results show that the survey precision of GPS is as high as 0.1mm on the hillslope,and is poor in the gully because of the sudden negative landform there.