Abstract: Objectives: The polar observation of the reflectance signals from various orbit types in the Beidou Satellite Navigation System III (BDS3) presents distinctive characteristics. This paper analyzes a 10-day simulation event of polar Beidou third-generation satellite navigation system reflectometry (BDS3 Reflectometry, BDS3-R) and proposes a novel spatiotemporal observation performance assessment method. Methods: Based on the concept of Knearest neighbors, a novel method for calculating temporal and azimuthal resolution is proposed. This research delves into the spatiotemporal performance of BDS3-R technology in polar observations, considering satellite orbit altitude and inclination. Results: The findings reveal that in the polar region (latitude > 66.34°), an increase in satellite orbit altitude leads to a gradual extension of revisit time and a reduction in spatial resolution. Specifically, at an orbit altitude of 800 km, the revisit period reaches approximately 35 hours, with an average spatial resolution of about 17.6 km. Furthermore, high-orbit satellites, such as GEO, demonstrate advantages in polar grazing observation events. Additionally, as the inclination of the BDS3-R orbit approaches 90 degrees, there is a gradual increase in the revisit period. However, BDS3-R exhibits blind areas in monitoring the polar center when the inclination is less than 80 degrees or greater than 100 degrees. Conclusions: Consequently, we recommend adopting a dual constellation design with inclinations of 70-80 degrees and 80-90 degrees. The analyses also show that polar observations tend to use larger reflector antenna inclinations and that pointing orientation has a significant effect on the number of reflection events. These research findings have substantial implications for future GNSS-R polar monitoring based on the BDS3 system.