In order to meet the reflectivity measurement requirements of any incident angle at different points of the large size special high mirror, a rotating cavity ring-down spectroscopy high reflectivity measurement system was built, in which the rotation function of the resonant cavity was set, and the lifting and parallel travelling mechanism of the measured mirror was added. Furthermore, the uncertainty of the measurement results was analyzed and calculated. The results showed that the reflectivity of a high reflective mirror measured by the system was 99.979 5%, the measurement accuracy reached the order of 10-6, and the combined standard uncertainty of reflectivity measurement was 0.002 8%. Collectively, these results provide a detection guarantee for the maintenance of the large size special high mirror, and provide ideas and methods for the uncertainty analysis of measurement results of similar equipment parameters.