An improved design method of a two-stage FRM filter includes the following steps: constructing an improved two-stage FRM filter; calculating passband and stopband edge parameters of a prototype filter, passband and stopband edge parameters of a second-stage masking filter and passband and stopband edge parameters of a first-stage masking filter in Case A and Case B, respectively; calculating the complexity of the FRM filter according to the obtained parameters, and finding out one or more sets [M, P, Q] having the lowest complexity within a search range; and optimizing the improved FRM filter. The improved design method of a two-stage FRM filter has the following beneficial effect: as compared to a conventional design method of a two-stage FRM filter, the complexity of a narrow-band FIR (Finite Impulse Response) filter can be reduced through design using the improved method, and power consumption is thus reduced in hardware implementation.