In order to understand the constellation configuration of BeiDou Navigation Satellite System Ⅲ and its global service performance, the third-generation constellation configuration of BeiDou was established. Using constellation usability and coverage assessment indicators, the performance of the Beidou third-generation constellation at 4 typical MGEX stations and the global observatory are simulated and evaluated respectively. The evaluation results show that there are an average of 14 stars and a mean GDOP of 1.41 in the global system of BeiDou. The performance of the Beidou system is equivalent to that of the GPS. The performance evaluation of the Beidou in 58.75°-160°E is obviously better than that of the GPS. The results of this evaluation can provide reference for the effective utilization of navigation and positioning services and the improvement of accuracy when the BeiDou Navigation Satellite System Ⅲ are fully completed.