Knife-edge method is one of the main methods to obtain the modulation transfer function (MTF) of X-ray detectors,while data processing is critical to the accuracy. A series of data processing methods is presented,which can improve the measurement accuracy of MTF for a high-resolution X-ray CCD. Before experiments,MTF simulation is employed to predict the curve trend and noise level. Subsection-analysis algorithm is used to analyze the curve fluctuation in order to eliminate the subjective errors. MTF is recorrected by the oblique angle of the knife edge,which is gotten by using self-adaptive algorithm,clip-window algorithm,and Hough transform. After all the procedures,the mean square deviation of 0.011 for the MTF is achieved,while the Nyquist frequency error is 2.52%.