Abstract: In the distortion detection of the lithography projection objective, the displacement measurement error is one of the important error sources. Depth analysis of the error sources and reduction of the error terms can improve the distortion detection accuracy. Combining the positioning and measurement technology of the moving stage, this paper analyzes the displacement measurement error of the image quality detection stage when the Shack-Hartmann wavefront sensor is used to detect the distortion of the projection objective. In this paper, a set of image quality detection platform is taken as an example to analyze the displacement measurement error in the distortion detection of the projection objective, and the image quality detection platform is used to measure the distortion of a projection objective. The distortion detection result is about 80 nm, in which the displacement measurement error of the image quality detection platform will bring about an uncertainty of about 22 nm to the distortion detection result.