Abstract: For poor precision single point positioning performance of single GPS system under Occlusion Condition,to improve performance of precision single point positioning cross multisystem in this paper, By setting different Elevation mask angle, the environment around the city is divided into normal environment, general occlusion and heavy occlusion. Using GPS, GPS／GLONASS, GPS／Galileo, GPS／GLONASS／Galileo different modes respectively, the static PPP simulation experiments were carried out on four continuously operating reference stations in hong kong under the environment. the results show that multisystem combination can effectively remedy the shortage of satellites in the occlusion environment around the city, and the PPP performance of GPS／GLONASS, GPS／Galileo, GPS／GLONASS／Galileo combination is improved to varying degrees compared with that of a single GPS system.