为了提高瑞奇-康芒法检测平面镜面形误差的精度，提出了利用检测系统光瞳面与被检平面镜表面的坐标映射关系插值拟合平面镜面形的方法。结合最小二乘法分析，解算了由光路调整引入的离焦误差，获得了更为真实的平面镜面形误差。理论仿真分析显示，此方法的平面镜测量误差可控制在λ/100(λ=632.8 nm)量级。对口径为40 mm的小口径平面镜进行了实际检测，检测过程中通过多角度旋转被测平面镜，利用坐标映射关系和幅值转换关系对测试波前进行恢复，在分离系统离焦误差后得到被检平面镜面形RMS值为0.018 6λ，与干涉仪直接检测得到的RMS值0.021λ相比，残差为0.002 4λ。实验结果证明了此种误差分离技术在瑞奇-康芒法对平面镜面形检测时的有效性与准确性。

To improve the accuracy of Ritchey-Common test for a flat mirror, a new method to use the relationship between the system pupil coordinate and the test mirror coordinate to interpolate and fit the test mirror surface was proposed. On the basis of the least square method, the system defocus error and surface error in two test angles were detached to gain a more actual flat surface error. The simulation analysis shows that the test error can be controlled under λ/100(λ=632.8 nm). A flat mirror with a diameter of 40 mm was tested. In the test process, the test flat mirror was rotated with different angels and the wavefront was reconstructed through the relationship between coordinate mapping and amplitude conversion. The obtained results show that the RMS of the test mirror surface is 0.018 6 λ after detaching the defocus error of the system. As compared with the test RMS of 0.021λ from an interferometer, the residual error is 0.002 4 λ . Experiment results indicate that this error detaching method is valid and accurate in the Ritchey-Common test for flat mirrors.