Abstract: The key premise of the low orbit navigation enhancement is to realize the whole network time synchronization of the low earth orbit (LEO) constellation. In order to solve the problem of real-time and high-precision time synchronization of LEO constellation, a high-precision time synchronization method based on real-time precise point positioning (RT-PPP) is proposed for LEO navigation augmentation system. This paper analyzes all kinds of errors in the process of processing, introduces the processing flow of real-time and high-precision time synchronization method of LEO satellite using state space representation (SSR) correction information and precise point positioning, and applies this method to the processing of measured data of constellation observing system for meteorology, ionosphere and climate (COSMIC) satellites. The results show that the standard deviation of orbit error is in decimeter level, and the standard deviation of clock error is about 2.4 ns and 2.3 ns respectively, which can reach nanosecond level. By comparing the results of different methods, it can be seen that the PPP method using SSR correction information is obviously better than the pseudorange method using broadcast ephemeris, and the accuracy is equivalent to the PPP method using post precise ephemeris.