###### Abstract  
The precise orbit determination (POD) for BeiDou satellites is usually limited by the insufficient quantity and poor distribution of ground tracking stations. To cope with this problem, this study used the GPS and BeiDou joint POD method based on Chinese national continuous operating reference stations (CNCORS) and IGS/MGEX stations. The results show that the 3D RMS of the differences of overlapping arcs is better than 22 cm for geostationary orbit (GEO) satellites and better than 10 cm for inclined geosynchronous orbit (IGSO) and medium earth orbit (MEO) satellites. The radial RMS is better than 2 cm for all three types of BeiDou satellites. The results of satellite laser ranging (SLR) residuals show that the RMS of the IGSO and MEO satellites is better than 5 cm, whereas the GEO satellite has a systematic bias. This study investigates the contributions of CNCORS to the POD of BeiDou satellites. The results show that after the incorporation of CNCORS, the precision of overlapping arcs of the GEO, IGSO, and MEO satellites is improved by 15.5%, 57.5%, and 5.3%, respectively. In accordance with the improvement in the precision of overlapping arcs, the accuracy of the IGSO and MEO satellites assessed by the SLR is improved by 30.1% and 4.8%, respectively. The computation results and analysis demonstrate that the inclusion of CNCORS yields the biggest contribution in the improvement of orbit accuracy for IGSO satellites, when compared to GEO satellites, while the orbit improvement for MEO satellites is the lowest due to their global coverage. precise orbit determination; ground tracking stations; BeiDou satellites; Chinese national continuous operating reference stations 20179 8103390/rs908081  
MEO satellites and about 3-4 m for BeiDou GEO satellites based on ground tracking stations [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. As a secondary orbit determination system, on-board GPS-based orbit determination in GEO can demonstrate a 3D positioning accuracy of about 1 m [17]. Several factors affect the precision of BeiDou POD, such as satellite orbit dynamic modeling, solar radiation pressure [2; 5; 6; 10; 14; 15; 16], albedo and antenna thrust, satellite attitude and maneuver [18; 19; 20; 21], and transmitting antenna phase center modeling [22]. Besides the factors mentioned above, the orbit determination method, as well as the number and distribution of ground tracking stations, play an important role in BeiDou orbit determination. In terms of the orbit determination method, [PERSON] et al. [2] analyzed the BDS single-system independent orbit determination method and found that the precisions of 3D overlapping arcs of GEO and IGSO satellites reached 3.3 and 0.5 m, respectively. Based on the two-step GPS-assisted BeiDou orbit determination method, [PERSON] et al. [3] achieved a radial overlap precision at the 0.1 m level for both BeiDou GEO and IGSO satellites. [PERSON] et al. [8] adopted the BDS/GPS joint orbit determination method. The 3D overlap precision of the GEO, IGSO, and MEO satellites reached 155, 33, and 28 cm, respectively, and the radial overlap precision was basically better than 10 cm. [PERSON] et al. [11] studied the precision differences of the BDS single-system orbit determination method and the GPS-assisted two-step orbit determination method, as well as the causes of such differences. In terms of the number and distribution of ground tracking stations, [PERSON] et al. [9] conducted several experiments on the impact of expanding the tracking geometry and the addition of MEO satellites on the BeiDou precise orbit. They concluded that expanding the geometry contributes to improving the BeiDou orbit's precision. Using the BeiDou Experimental Tracking Stations (BETS) and the International GNSS Service (IGS) Multi-GNSS Experiment (MGEX) network stations for BeiDou orbit determination, [PERSON] et al.