The reflectivity measurement on high reflective mirrors in the mid-and-far infrared range was performed based on the Cavity Ring-down (CRD) technique. A pulsed quantum cascade laser with center wavelength of 9.7μm was used as the light source in the experimental setup,with which the reflectivity of the cavity mirrors at different cavity lengths was measured. The reflectivity was determined statistically to be 99.946 4% and the measured repeatability error is better than ±0.001 4%. The experimental results indicated that the CRD setup has a high repeatability and accuracy,and can be applied in high reflectivity measurements of mid-and-far infrared mirrors.