When measuring the modulation transfer function (MTF) of CCD camera with rectangle target, the test value of MTF is less than the actual value due to the initial position error and the initial angle error between the target and pixels of CCD. With the definition of MTF, the luminance distribution of CCD pixels is deduced and the relationship between MTF and the initial errors is given. The results with initial position and angle errors are analyzed. The formula of initial angle error is deduced by using the luminance of pixels and the result is verified by simulation.