Abstract: In the relative positioning baseline calculation process, selection of the coordinate position of the control network constraint point has a certain impact on the data calculation accuracy. This paper discusses the site selection method of the control network configuration considering the minimumgeometric factor of precision (GDOP), the selection of 6 constraint point reference stations for the global MGEX (Multi-GNSS Experiment) stations, and the use of BeiDou-2/BeiDou-3 (BDS-2/BDS-3) actual measurement data to compare the results of 18 Interactive Generator of Multimedia Application System (iGMAS) stations around the world. The station coordinates are calculated and compared with the accuracy of the results of the global grid-based random station selection method. The experimental results show that compared with the grid-based random station selection method, when the GDOP value selection method is used to calculate the relative positioning baseline, the standard deviation of the baseline length above 6 000 km can be increased by about 7 mm. For the long baseline, the standard deviation accuracy in east (E), north (N), up (U) can be increased by about 5 mm; the position accuracy of the pending point can be increased by about 40%. It can be seen that GDOP method can improve the relative positioning accuracy of BDS-2/BDS-3.