A microwave photonic filter based on photonic crystal fiber Sagnac loop was presented, the filter′s center frequency can be continuously tunable. The length of photonic crystal fiber is 5m, using the thermo-sensitive liquid of Cat.19340 to fill one big hole of photonic crystal fiber and then embed it into Sagnac loop. The effect of different duty ratios to the period of comb spectra of Sagnac loop and the tuning range of the passband center frequency of the filter were analyzed. The measured results show that the larger the duty ratio, the smaller the period of comb spectra of Sagnac loop and the larger tuning range of the passband center frequency of the filter. In the case of the maximum duty ratio, the simulation measured period of comb spectra of Sagnac loop at the temperature of 20℃ and 80℃ are 0.72 nm and 0.52 nm respectively. Using the Sagnac loop to slice the broadband light source, by adjusting the thermo-sensitive liquid′s temperature from 20℃ to 80℃, the center frequency of the microwave photonic filter can be tuned continuously within the range of 15.5 GHz ~21.5GHz.