Abstract We evaluate the precision of broadcast ephemeris of BDS-2 and BDS-3 using precise ephemeris products. We further compare and analyze the influence of different BDS-2 and BDS-3 constellation combinations on single point positioning(SPP). We propose a SPP weighted optimization model based on SISRE(signal in space range error). The experimental results show that the broadcast ephemeris orbit errors of MEO, IGSO and GEO satellites in BDS-2 constellation are 2.404 m, 3.030 m and 12.574 m respectively. The broadcast ephemeris orbit errors of MEO and IGSO satellites in BDS-3 are about 0.5 m and 0.8 m respectively. For SISRE, BDS-2 is on average better than 2 m and BDS-3 is on average better than 1 m. BDS-3 satellite clock error and stability with H clock and Rb clock are basically the same. At the same time, SPP results show that BDS-2/BDS-3 IGSO/MEO constellation combination has the highest positioning accuracy. The SISRE weighted model is used to solve the SPP, and the optimized positioning accuracy is 9.61%, 18.55%, and 11.19% respectively in the N,E,U directions, proving the effectiveness of the model.