Abstract: Based on optical element’s high precision in-situ measurement requirements, this paper carries out the sensitive factor simulation analysis, studies the influence of systematic structural errors and temperature errors on the measurement results, and designs and builds an in-situ measurement device to carry out measurement experiments of system temperature change, system repeatability and system stability. The results show that the simulation detection model can be used for plane/spherical/aspherical/free surface, the influence on the measurement results is mainly reflected in the low frequency error, the high frequency error is relatively small, the maximum PV value of the measurement surface shape error does not exceed 68nm (about λ/10), and the maximum RMS value does not exceed 15 nm (about λ/40).