In view of the difficulty of BeiDou Navigation Satellite System(BDS) global continuous monitoring and the long convergence time of Global Navigation Satellite System(GNSS) precision positioning, a global navigation augmentation system based on Low Earth Orbit(LEO) communication constellation is proposed. The system can be developed together with the LEO communication system, and needn’t build a new system. The LEO satellites can jointly determine the precise orbits and clock errors of GNSS satellites and LEO satellites with the data from the mounted high precision GNSS monitoring receiver and the ground based monitoring stations. When served as navigation information broadcasting sources, besides the precise orbit, precise clock error, and integrity augmentation information, an additional navigation augmentation signal is broadcasted to realize Global Precise Point Positioning(GPPP) with sub-meter level of positioning precision in dynamic mode and sub-decimeter level of precision in static mode. The convergence time of precise point positioning is cut from 30 min(using a GNSS system alone) to less than 5 min(using a GNSS system together with the LEO global navigation augmentation system).