Abstract: The satellite navigation system and inertial navigation system are highly complementary, the integration of the two systems can improve the usability, continuity and reliability effectively. With the rapid development of the BeiDou system and the continuous improvement of the performance of low-cost MEMS IMU, the study on the theory and technology of integrated navigation system based on BDS and low-cost IMU has strong research significance and practical value. Firstly, the theoretical model of BDS RTK/M-EMS INS is deduced, and the performance of the integrated system is analyzed using the measured vehicle data. The experimental results show that introducing low-cost IMU into BDS can effectively improve the precision of velocity measurement without losing the positioning precision. The positioning accuracy in the vehicle dynamics is mm level, and the RMS of velocity error improvement has reached to 75.8％, 79.5％, 66.7％ in the north, east, and vertical components respectively. Moreover, using dual-frequency data in the tightlycoupled integration of BDS+INS can further improve the precision of velocity and attitude measurements, the RMS of velocity error improvement has reached to 18.2％, 33.3％, 33.3％, the RMS of attitude error improvement has reached to 41.1％, 26.7％, 59.0％.