The aperture of optical imaging detecting system is larger and larger

so local defects is more likely to occur during the optical manufacturing.Influence of position of local defects distribution on the optical system is analyzed.Modulation transfer function（MTF）based on imaging optical system

the effect of the position distribution of defects on spacial frequency is analyzed theoretically.The property of MTF influence of a real defect is analyzed by Zemax and Matlab.Results indicate that the adverse effect of defects on high frequency is avoided

the cut off frequency is increased 5 %.