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Modulation Transfer Function (MTF) is a widely used parameter to assess the on-orbit performance of satellite optical sensors. As one of the most widely used on-orbit MTF estimation methods, the target of knife-edge method is relatively easy to deploy or select, and its data processing is straightforward and can achieve reasonable estimation results. Unfortunately, its estimation accuracy is greatly influenced by many factors and not enough emphasis has been placed on the quantitative analysis of their influences, which limits the creditability and application of estimation result. Therefore, this paper focuses on the implementation and accuracy analysis of the knife-edge method. It begins with a discussion on the necessity and importance of carrying out on-orbit MTF estimation, and the advantages and unresolved problems of the knife-edge method are also analysed. Secondly, the principle, requirements of target and basic data processing steps of the knife-edge method are presented. Thirdly, the influences of major factors affecting the accuracy of MTF estimation result based on the knife-edge method is emphasized using theory analysis and simulation experiments. The analysed factors include atmosphere, the incline angle of target, the contrast and random noise of target, the edge detection accuracy, and the Edge Response Function (ERF) curve-fitting model. The analysis results can provide pivotal guidelines to implement on-orbit MTF estimation based on the knife-edge method. The overall accuracy of on-orbit MTF estimation based on the knife-edge method is also explored using simulation experiments, which provide statistics about the accuracy of MTF estimation results. Finally, an experiment using three knife-edge targets in SPOT-5/Pan image of Dalian airport with different contrasts, signal-to-noise ratios and incline angles is carried out, and its relatively consistent results strongly support the validity of the knife-edge method.