Real-time orbit determination simulations were conducted using the space-borne GPS/BDS (BeiDou navigation satellite system) receiver developed for the ZDPS-3 mission. The orbit determination performance based on BDS, especially the B3 frequency, was evaluated. As results, with the higher chip rate, the anti-noise performance of pseudo-noise code of B3 was obviously better than that of B1, which can be utilized to achieve a better orbit determination accuracy. Based on the establishment of the observation model and the orbit determination algorithm model, a hardware-in-loop simulation experimental platform was established after the quality of the receiver’s field observation data was evaluated. The simulation results show that, under the same conditions, the real-time orbit determination accuracy of the B3 frequency is better than that of B1, and comparable to that of GPS in full operation.