In GPS / BDS combined system, the regression period of MEO orbit satellite of BDS system is different from that of BDS (GEO, IGSO) / GPS orbit satellite, which shows that the corresponding sidereal daily filter model is not unique, and the multipath error suppression effect is also different. In order to achieve better deformation monitoring effect, CEEMDAN-WT joint filtering was used to eliminate the noise effect of the baseline coordinate sequence, and then a sidereal daily filtering model suitable for GPS / BDS combination was constructed. Based on the multipath information extracted from the model, the multipath error of the baseline sequence of the next day was corrected. The measured results show that the horizontal positioning accuracy of baseline is less than 5 mm, the elevation positioning accuracy is less than 1. 33 cm, and the overall positioning accuracy is improved over 40% after the multipath error is suppressed by the sidereal daily filtering model combined with BDS (GEO, IGSO) and GPS.