Abstract: The traditional frequency response masking (FRM) filter consists of multiple filters with multiplier unit, which has a relatively high computational complexity. In this paper a method of improving the design complexity of narrow-band low pass FRM digital filter is proposed, in which the cascade integrator comb (CIC) filter is used as the masking filters to satisfy the design requirements of narrow transition band and to lower the computational complexity filter. The results of simulation show that this method is quite effective in reducing the computational complexity of narrow-band low pass FRM filter and in reducing the use of the multiplier units and the order of the target filter. Therefore, this method can be used in the design of narrow transition band FRM digital filter.