Frequency Correction Channel（FCCH） detection is very important to the synchronization of GSM frequency hopping digital repeaters and the demodulation of broadcast information from the base station.This paper analyses the structures of FCCH and Synchronization Channel（SCH） pulses in GSM public control channels and introduces a FFT-based algorithm for the fast FCCH detection method.Simulation results indicate that this method can accurately capture FCCH and reduce the range of SCH search so as to synchronize the system quickly.