A microwave photonic filter based on a photonic crystal fiber sagnac loop comprises a broadband light source, a sagnac loop, a coupler B, a spectrum analyzer, a phase modulator, an analog signal generator, a single mode fiber, a photoelectric detector and a spectrum analyzer. The sagnac loop is composed of an sdB coupler A, a polarization controller and a liquid-filled photonic crystal fiber; the photonic crystal fiber of the sagnac loop is filled with liquid, the birefringence is changed by changing the temperature, the wavelength interval of the sagnac loop transmission spectrum is affected, the wavelength interval of input light is changed accordingly, and the filter passband center frequency can be tuned continuously. The microwave photonic filter has the advantages that the microwave photonic filter is simple in structure and easy to implement, the photonic crystal fiber of the sagnac loop is filled with liquid, the temperature is changed, the continuous tuning of the filter passband center frequency can be implemented, the dynamic response range is large, the manufacture technology is mature, cost is low, and the promotion and application are benefited.