As an important part of China’s first Mars exploration mission， the Tianwen-1 relay communication system is responsible for providing efficient and reliable communication services between the lander-rover and orbiter， and supporting the completion of exploration mission during the entry， descent and landing （EDL） phase and on Mars’ surface. The relay communication scheme of Tianwen-1 probe with ultra high requency（UHF） band is introduced. The composition， specifications and design method of the critical part of the relay communication system are given. The results of on-orbit flight data are analyzed. The flight verification results show that the newly developed relay communication system of Tianwen-1 probe successfully achieves the exploration mission objectives. Its design， implementation and application also provide technical reference for the subsequent development of China’s deep space relay communication system.