Abstract：To take full advantage of BDS-3 and Galileo multi-frequency signals on positioning, we make a proper selection of BDS-3 and Galileo four-frequency wide-lane combinations, and construct multi-frequency positioning models which are suitable for BDS-3 single-system, Galileo single-system, BDS-3/Galileo dual-system as well as BDS-3/Galileo/GPS triple-system, based on the proper combinations. We compare and analyze the multi-frequency long baseline data, positioning accuracy and stability of four positioning models. The results show that when the long-baseline is over 500 km, the positioning accuracy of the BDS-3 single-system is better than that of the Galileo single-system. The positioning accuracy of the BDS-3/Galileo dual-system can reach the decimeter level in both the horizontal and vertical directions, which is more than 10% and 25% higher than that of the BDS-3 single-system, and the stability is also significantly improved. Compared with the dual-system, the positioning accuracy of the BDS-3/Galileo/GPS triple-system is improved by about 10%. The relative positioning accuracy of the dual-system and the triple-system reaches 1×10-9 m, which can meet long-baseline precise positioning requirements. The increase of satellite systems not only increases the number of visible satellites, but also enhances the geometry of the satellites, which improves the positioning accuracy and stability effectively.