The invention discloses a frequency sharing method and a device of a wireless communication system based on the OFDM. The wireless communication system based on the OFDM comprises a base station and a mobile device which work in a wireless band. The method includes that interference signals in the wireless band are detected; the base station sets interference indication information in control words of descending frames to be sent to the mobile device according to the interference signals, and the interference indication information expresses an occupied frequency band of the interference signals in the wireless band; and the base station sends the descending frames to the mobile device, so that the mobile device can avoid the frequency band where the interference signals are in according to the interference indication information. According the wireless system of the frequency sharing method and the device of the wireless communication system based on the OFDM, additional frames are not needed to be produced for broadcasting the interference indication information, interference from other unknown systems working in a same wireless band can be avoided, and further, spectrum resources can be fully used.