The invention discloses a radio frequency back-up device used for a multi-system communication system, which is structurally characterized in that various main signal channels and standby signal channels in different systems simultaneously enter a device A which merges the signals with different systems and uniformly inputs the signals into a device B, the device B has the main function of switching the input main signals and the input standby signals so that the main signals and the standby signals in different systems can respectively enter a corresponding system device C, and the device C respectively sends the signals in different systems to respective antenna ports for covering the same region.