氧碘腔镜作为氧碘化学激光器重要组成部分，氧碘腔镜反射率的高低制约氧碘化学激光器功率的提高，必须对氧碘腔镜反射率进行精确测试。基于光腔衰荡光谱法搭建的氧碘腔镜高反射率测量系统测量精度高，氧碘腔镜中450全反镜反射率测试结果为99.979%。搭建的氧碘腔镜高反射率测量系统的不确定度主要由衰荡腔腔长、腔镜衰荡时间和待测镜衰荡时间时间确定。其中衰荡曲线最大幅值点的选取和测量重复性对测量结果的不确定度影响较大，在对衰荡曲线的处理过程中，应该注意选取合适的幅值点。通过对氧碘腔镜高反射率测量系统不确定度分析，得出扩展不确定度为0.0152%。

Chemical oxygen iodine Laser (COIL) power is restricted by the reflectivity of COIL mirrors who are important parts of COIL, so the reflectivity of COIL mirrors must be tested precisely. The precision of measurement system is high for the high reflectivity of COIL mirrors based on cavity ring-down spectroscopy, the reflectivity for an 45° optical mirror of COIL mirrors is 99.979%. Uncertainty of measurement system for the high reflectivity of COIL mirrors are based on cavity ring-down length, cavity mirrors ring-down time and tested mirrors ring-down time. By studying the vertex of curve ring-down and tests repetition, it is found that vertex of curve and tests repetition are sensitive. When ring-down curve is managed, the vertex of curve is properly choosed. Uncertainty analysis of measurement system for the high reflectivity of COIL mirrors has been done, expanded uncertainty is 0.0152%.