Abstract: A ring frequency shifter based on the photonic crystal fiber was proposed. Based on Brillouin frequency shift theory, the frequency shifter could achieve a narrow linewidth and high-gain laser output for the photonic crystal fiber which had high Brillouin gain and low threshold, using the frequency selecting amplification technology of fiber optic ring resonator. The experiment results show that the threshold power of stimulated Brillouin scattering(SBS) of photonic crystal fiber is 457 mW, the frequency shift of stimulated Brillouin scattering wave compared with the incident light is 9.778 GHz with linewidth less than 500 kHz, the frequency shift can be finely adjusted by temperature. The frequency shifter can be applied in the distributed fiber optic Brillouin sensor and microwave generator.