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In this paper a joint timing and frequency synchronization method based on Fractional Fourier Transform(FrFT)is proposed for Orthogonal Frequency-Division Multiplexing(OFDM)system.The combination of two chirp signals with opposite chirp rates are used as the training signal,the received training signal with timing and frequency offset is transformed by FrFT and the two peaks representing two chirps in FrFT domain are detected,then the position coordinates of the two peaks are precisely corrected and substituted into an equation group to calculate timing and frequency offset simultaneously.This method only needs one FrFT calculation to implement synchronization,the computational complexity is equal to that of FFT and less than that of correlation or maximum likelihood calculation of existing methods,and estimation range of frequency offset is large,greater than half the signal bandwidth,while the simulation results show that even at low SNR it can accurately estimate timing and frequency offset and the estimation error is less than that of existing methods.