A precise single point positioning method based on the fusion of BDS/GPS/GLONASS is presented, unifies the time system and space system of three systems combined precise positioning, establishes the non difference combination model of precise single point positioning, and uses the observation data to solve the precise single point positioning. The calculation results show that compared with a single system, the combination of three systems can effectively shorten the positioning convergence time and improve the positioning accuracy when the number of satellites in a single system is small or the distribution of satellite constellations is poor. It has more advantages in terms of continuity, availability, reliability, accuracy and efficiency.