For a given chirp phase mask, only comb filter with special channel spacing can be fabricated. A novel approach to implement arbitrary channel-spacing comb filters based on direct current (DC) phase shift in fiber Bragg grating (FBG) is proposed. Arbitrary channel-spacing comb filter can be achieved by a single chirped phase mask and a submicrometer-precision translation stage. The proposed method is cost-effective, flexible and simple compared to traditional ways. Simulation and experiment show that arbitrary phase shifts introduced by DC refractive index modulation can be achieved. Multichannel comb filter with channel spacing of 100, 50, 40 GHz are implemented with a same phase mask. The impact of DC phase shift length and phase errors on side band suppression ratio are also analyzed.