中文摘要：

基于STK软件对COMPASS、GPS和GLONASS系统进行不同程度的组合仿真，在中国区域内，从卫星可见数、PDOP值以及定位精度进行分析。结果表明，在给定标准定位服务下各系统UERE值的情况下，三系统组合在我国的定位精度达5～6m，PDOP值达0．8～0．9，优于各双系统组合，而双系统组合又优于各单一系统；同时三系统组合下的PDOP值降低，定位精度更高，波动更加平缓。

英文摘要：

This paper carried out different levels of combined simulations of COMPASS, GPS and GLONASS systems based on the STK software, and analyzed the data of the visible satellites number, PDOP value and the po- sitioning accuracy in China region. Simulation results indicate that： with the given UERE value of the various sys- tems in the Standard Positioning Service, the positioning accuracy of the combination of three systems is 5-6 m, and PDOP value is 0.8 - 0.9, which is better than the combination of dual systems, while the combination of dual sys- tems is superior to the single system. Meanwhile, the results also show that the PDOP value in combination of three systems is lower and the positioning accuracy is higher, and the fluctuations are more gentle.