Abstract: At present, the BDS-3 system has been built and provides open services for users worldwide. With the expansion of BDS service scope, the application of BDS positioning technology is gradually increasing, so the positioning performance of BDS is particularly important. Based on the measured data in Tianjin, the Extended Kalman Filter (EKF) and MLAMBDA algorithm are used to compare the RTK positioning performance of BDS, GPS and BDS/GPS from satellite visibility, PDOP and positioning error. According to the experiment：?Under the static baseline, the plane positioning accuracy of BDS RTK is about 3.25cm, and the vertical accuracy is about 5.98cm. ?Under the dynamic baseline, the worst positioning accuracy of BDS RTK is less than 9cm.It shows that the positioning accuracy of BDS can reach centimeter level without relying on other satellite systems, which is enough to meet the needs of daily mapping and positioning. The above research provides relevant reference information for BDS users.