Abstract: In this paper, a space-based orbit determination and time synchronization method for Earth-Moon spacecraft was presented. As a “space-based tracking station”, LEO satellite on the one hand receives GNSS navigation signals to achieve high-precision real-time orbit determination and timing; on the other hand, it establishes measurement links with Earth-moon space spacecraft to support the fast and high-precision orbit determination of Earth-moon spacecraft. Compared with ground stations, LEO satellites operate at a faster speed and orbit the Earth in a shorter period. The Earth-Moon spacecraft and its measurement link have the advantages of short invisible time interval, better measurement geometry, and no atmospheric delay in the measurement process. Therefore, using LEO satellite can improve the convergence speed and accuracy of orbit determination. This paper analyzed the space-based orbit determination and time synchronization performance of three typical orbits in Earth-Moon space, including the distant retrograde orbit (DRO), the highly elliptical orbit (HEO) and the Earth-moon transfer orbit. Space-based orbit determination simulation results show that when the LEO satellite position accuracy is high, the convergence time of the three orbits is less than 3 hours, the orbit position accuracy is about 50 m, and the time synchronization accuracy is tens of nanoseconds. Therefore, this method can hopefully solve the problems of limited deployment and heavy burden of ground stations.