The present invention discloses an OFDM signal demodulation method and device thereof. The method comprises: adding a pre-obtained timing offset estimation value of an OFDM signal demodulation device to the initial position of an OFDM symbol of a received signal to obtain a window deviation value of the OFDM symbol; adding a channel time delay extension to the window deviation value to obtain a combined prefix initial position; calculating the combined OFDM signal value starting from the prefix initial position; processing the Fast Fourier Transform (FFT) for the combined OFDM signal value to obtain a frequency domain data subcarrier signal; calculating the frequency domain original channel estimation value processing the channel estimation based on the original channel estimation value phase modification of the OFDM symbol according to the channel estimation compensation indication value; and processing equalization and detection for the frequency domain data subcarrier signal according to the channel estimation result. The present invention uses the cycle prefix of the received signals to promote the demodulation performance of the OFDM signal demodulation device.