Abstract: Using Kalman filtering algorithm in GPS-based orbit determination for LEO,we have to deal with an observation mode and a dynamic model.GPS broadcast ephemeris algorithm will be regarded as the dynamic model of kinematic filtering.Firstly,the fitting algorithm for GPS broadcast ephemeris parameters is introduced.Then,the advantages and disadvantages of geometric orbit determination are analyzed.Finally,a new adaptively robust synthetic orbit determination algorithm is developed based on the predicting characteristic of GPS broadcast ephemeris algorithm and the adaptively robust filtering principle.The results show that the adaptively robust synthetic orbit determination algorithm can not only make good use of the geometric observation information but also reasonably adjust the contributions of the geometric observations and ephemeris predicted information to the filtering solution.