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Global navigation satellite systems (GNSS) are mainly using MEO satellites and the regional augmentation systems are primarily using GEO satellites at present.The signal strength is very weak due to the satellite to earth propagation loss when the navigation signals reach the ground.The weakness of the satellite navigation embodies in frequently losing lock due to signal occlusion caused by some sheltering effect and electromagnetic interference.LEO satellites have inherent advantages in improving the power of the receiving signal at the same transmitting power.The navigation availability for the users in the complex environment can be improved significantly.With the booming development of the small satellites and micro satellites,hundreds of small satellites will be launched in the future 5-10 years.It can be predicted that the inherent weakness of the present GNSS system can be remarkably ameliorated if LEO satellites integrate navigation services and fuse with the GNSS.This paper proposes architecture of global navigation augmentation and backup using LEO satellites.Two important aspects are embodies as follows: (1) augmentation,LEO satellites and GNSS are networked to largely improve the positioning precision,availability and integrity; (2) backup,the LEO satellite constellation can provide independent navigation service when the GNSS could not be used due to signal blockage or electromagnetic interference.A developing LEO satellite constellation is used in the analyses and simulations.Simulation results emerge that the proposed space-based global LEO augmentation and backup navigation system can effectively enhance the performance of GNSS service.It is forecasted that real-time global precise point positioning service can be provided in the future.The navigation precision using LEO satellite alone can reach a precision about 10 meters,and it can play the role of a backup system to the GNSS system.The researching results in this paper can be used in the design and construction of the PNT hierarchy in our country.