In recent years, Unmanned Aerial Vehicle (UAV) technology has developed rapidly, and there are more and more UAV applications for IOT scenarios. Considering the scarcity of frequency resources, UAV systems can be considered for cofrequency multiplexing with terrestrial mobile communication networks. In the UAV with IOT terminal scenario, the airborne terminal transmitting to the ground may interfere with other services in the adjacent frequency. Therefore, this paper focuses on analyzing the interference of UAV system in 1800MHz band to the base stations and terminals of TDD private network system in neighboring frequency, and derives the isolation distance required for system coexistence in different interference scenarios. Finally, reference interference mitigation measures are given based on the analysis results.