The present polling time division duplex (PTDD) ranging hierarchy of GPS inter-satellite links (ISL) demands being optimized for satellite orbit determination. An improved ranging hierarchy named grouping time division duplex (GTDD) is presented. Satellite orbit determination precision based on inter-satellite and satellite-to-station ranges is able to be improved by the novel ranging hierarchy in respect of ISL ranging links increasing by grouping ranging of the whole constellation. Aiming at the optimal satellite orbit determination precision, a two-steps algorithm is presented to optimize the satellite grouping. Firstly, the optimal satellite groupings were obtained to achieve the most inter-satellite ranging links. Secondly, the ranging DOP was made the least in each satellite group. Simulation results show that the satellite orbit determination precision can be improved greatly from the two-steps algorithm.