Abstract: With the completion of BDS-3 in China, the requirements of high-precision positioning and attitude determination based on BDS-3 is increasingly urgent. This paper derives the BDS-3 precise point positioning(PPP)model with ionosphere-free combination and inertial navigation system(INS)error equation in geocentric fixed coordinate system , and constructs the BDS-3 PPP/INS tight combination filtering model. This paper evaluates the positioning performance of BDS-3 PPP, BDS-3 PPP/INS loose combination model and BDS-3 PPP/INS tight combination model. The results of the experiment show that the position accuracy of BDS-3 PPP/INS loose combination is basically the same as that of BDS-3 PPP, the position accuracy of BDS-3 PPP/INS tight combination model in the east, north and sky directions is 7.9 cm, 9.3 cm and 9.4 cm, which is higher than that of BDS-3 PPP/INS loose combination model by 38.3%, 33.1% and 35.6%; the speed is improved by 27.3%, 45.8% and 12% respectively in three directions; the attitude accuracy of both is equal.