Overview: Lithography accuracy is one of the key parameters to measure the lithography process. Lithography projection objective is the core component of a lithography machine. The distortion of the lithography projection objective is one of the most important factors that affect the overlay accuracy. It causes the position offset exposed on the silicon wafer from the ideal position to the actual position. At present, the detection techniques for the distortion of the projection objective are exposure measurement, aerial image measurement, and wavefront measurement. The exposure measurement that is suitable for lithography manufacturers depends on the exposure process and equipment, thus its detection process is complex. The repeatability of exposure measurement is better than 1 nm. Both the aerial image measurement and the wavefront measurement without exposure are based on the photoelectric sensors. Its detection speed is fast, and the measurement accuracy can be better than 0.4 nm. The image quality detection platform of the projection objective is a device for detecting the optical performance of the projection objective. The wavefront sensor is a device for measuring wavefront aberrations and can also be used for distortion measurement. According to the principle of distortion measurement, when the Hartmann sensor is used to detect the distortion of the projection objective, the measurement accuracy of the mask's actual imaging position through the objective directly affects the accuracy of the distortion detection. So this paper focuses on the analysis of the displacement measurement errors of the image quality detection platform when using the Shack-Hartmann sensor to detect the distortion of the projection objective. The factors that affect the displacement measurement accuracy of the image quality detection stage mainly include the following aspects: the measurement error of the dual-frequency laser interferometer, the horizontal Abbe error of the distortion measurement, and the reproducibility error of the Hartmann position measurement. The measurement errors of the dual-frequency laser interferometer include the instrument error, the geometric error, and the environmental error. These errors are related to the performance of the interferometer, the layout of the interferometer, the performance of the image quality detection stage, and the environmental conditions. The horizontal Abbe error in distortion measurement is due to the fact that the dual-frequency laser interferometer cannot accurately measure the position coordinates of other points outside the central field in distortion detection. The reproducibility error of the Hartmann position measurement means the reproducibility of the Hartman sensor position information measured aiming at a same objective in a period of time. The factors that affect the reproducibility error of the Hartmann position measurement include the fluctuation of the interferometer value, the position control accuracy of the motion stage, the long-term drift of the interferometer, the long-term stability of the Hartmann sensor, the longterm stability of the test light source, the optical properties stability of the objective, etc. In this paper, a set of projection objective image quality detection platform is taken as an example to analyze the errors of its displacement measurement. Its displacement measurement error is about 22 nm within the measurement range of 40 mm × 40 mm. At the same time, the distortion of a projection objective is detected by this image quality detection platform, and the measurement result is about 80 nm. The displacement measurement error in the distortion detection of the lithographic projection objective is one of the important error sources of distortion detection. Depth analysis of the error sources and reduction of the error terms can improve the distortion detection accuracy.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.