To improve the precision of traditional high-reflectivity measurement technology, we propose a high-reflectivity measurement method based on the coupled cavity ring-down technique. We introduce an intracavity mode monitoring module into the coupled cavity ring-down system to determine the state wherein the coupling efficiency between the initial cavity and the measured cavity is consistent. Subsequently, more precise measurements under the fundamental transverse mode condition of the cavity are achieved. The experimental results show that the intracavity equivalent loss remains almost the same while the initial cavity and the measured cavity are solely operating in the fundamental transverse mode. For the same high reflectance sample, the measurement precision of the coupled cavity ring-down technique can be 10.0%--27.1% higher than that of the traditional method.