A method, which turns the direct estimation of wide difference in frequency into the estimation of period of a known sequence for the digitized demodulation of multi-channel signals, is presented. The wide frequency difference problems difficult to solve by available algorithm for actual demodulation can be simply estimated and rectified by the method. So, the difficult problem for the presently digitized demodulation is better solved. The method is simple in algorithm and needs less computation. And the method is especially applicable to the digitized demodulation of multi-channel signals. The simulation results suggest that the algorithm is practicable.