Abstract:   The mechanism of BDS／GPS multipath effects and the corresponding elimination and weakening measures are described respectively in this paper. The statistical analysis method is used to analyze the BDS／GPS multipath effects of monitoring points in complex environments during bridge deformation monitoring. Moreover, the influences of bridge tower, cable, traffic flow on BDS／GPS multipath error are also investigated. According to the measured data, the following conclusions are drawn: compared with BDS satellites, the multipath effect value of GPS, is basically the same as that of IGSO satellite but larger than that of GEO satellite and superior to that of MEO satellite; the multipath error is negatively correlated with the satellite elevation angle; bridge tower, cable and traffic flow are key factors of the multipath effects.