Abstract: BDS(BeiDou Navigation Satellite System) is the first heterogeneous constellation and the only currently fully operational tri-band navigation system. However, the international and domestic market is still dominated by GPS(Global Positioning System), since BDS starts relatively late. Because of the differences between BDS and GPS in space-time reference frame, constellation structure, signals and data quality, the existing high precision GPS data processing software can not directly deal with the BDS data. In order to realize high precision BDS positioning, the corresponding BDS data processing software must be developed as soon as possible. In this paper, the key issues of BDS/GPS high precision relative positioning are studied, and static relative positioning algorithm model is proposed. Moreover, this paper introduces a self-developed high precision BDS and GPS baseline processing software BGO(BDS/GPS Office), which contains BDS, GPS and combined baseline processing modules. The software is applied to process a CPI control network of high speed railway. The results show that BDS baseline precision is better than 1 mm in X and Z direction, and is better than 2 mm in Y direction. The experiment indicates that BDS baseline solutions meet the requirement of high speed railway CPI data processing. GPS baseline solutions from BGO are equivalent to the results from TGO(Trimble Geomatics Office) and Bernese software, and BDS/GPS combined baseline solutions from BGO are well-matched with the solutions from TBC(Trimble Business Center) software. Comparing BDS and GPS alone system, BDS/GPS combined could improve qualified rate and precise of baseline solutions.