To measure the Modulation Transfer Function (MTF) based on the theory of frequency spectrum is one of methods to rapidly evaluate the image quality of near-to-eye display system. However, some parameters during the rapid measurement have an obvious impact on the experiment results. So eliminating and offsetting the dispersion are the mostly factors when the method can be applied to measurement successfully or not. Reasons that may cause the error during measurement are analyzed specifically, and then influence degree of errors and method of discriminating clarity are discussed. Analysis of the main errors affecting the measurement of Contrast Transfer Function (CTF) shows that error value is below 3% when the tilt angle is within ±0.5°, brightness of light changes in the range of 0.6I~I, (I is the maximum value when the CCD works in the linear region) and object length changes within 5 mm, and the errors are all less than 1.5%. The experiment results verify the feasibility and practicability of the method and have the instructive significance on improving measure precision.