An optical comb filter based on the Sagnac ring loop is proposed. The comb filter response function is generated on the basis of the birefringent effect of the polarization maintaining fiber (PMF) within the loop. By utilizing the radio frequency (RF) signal along with the direct current (DC) to drive the phase modulator (PM) inserted in the Sagnac loop mirror, the independent tunings of the notch depth and filtering wavelength are realized. The response function of the proposed Sagnac filter is expressed theoretically with Jones matrix, and the effects of the optical filter notch depth and filtering wavelength on RF signal and the DC bias are analyzed. Based on the analysis results, the experimental link is set up to verify the theory. The results show that the tunable range of the notch depth from 0 dB to 30 dB is achieved. Besides, the filtering wavelength influenced by the DC from 0 to 12 V is continuously adjustable in the free spectral range (FSR) of 0.5 nm, and the wavelength tuning efficiency is 0.043 nm/V.