Abstract: Aiming at the problem of phase error caused by normal filters in signal processing, this paper summarizes the important meaning of digital filtering with zero-phase error, and introduces the all phase method as a new design method of digital filter with zero-phase based on the two traditional methods, that is FRR and RRF methods. And gives the demonstrations on the simulation experiments about the three methods, solving the problem of phase error in digital signal processing. It points out that all phase method is a good method of designing zero-phase digital filter, and this method is mechanically realizable but the two tradition methods can not on analyzing and comparing the three design methods. Finally, recommends the implement fields of the all phase method as a new method of designing digital filter.