Abstract: Through more than 200 measuring points with control parameters from different GPS control stations,we calculated,using random soft ware,the 3D coordinates of a single measuring point(ie,x,y,h),the measured distance between the points and control stations,and the difference between the coordinates and that between elevation values,showing the relationship between the distance and the difference is not a linear relationship.Thus,in the process of follow-up work of this project,we will extend the control radius to as long as 80 km(the test distance ranges in 0～88.621 km).Therefore,we suggest that the future GPS positioning survey should have a comparison between controlling radius.The methods used may be different for different areas.In addition,the method adopted should meet the requirements stipulated in the "normat ive" and "task document".