With the development of satellite communication and ground mobile communication system, the compatibility between them has aroused widespread concern. In this paper, a narrow-band cavity filter with high suppression is designed, which aims to suppress the passage of 5G interference signals in the frequency band of Beidou RDSS receiver. According to the constraint conditions, the order, zero configuration and topological structure of the filter are determined by CoupleFil software, so as to obtain the coupling bandwidth and quality factor, and then the filter is modeled and simulated by HFSS software combined with parameters. Finally, the simulation and physical test results meet the requirements, and have a good suppression effect on 5G mobile signals.