Abstract: Image quality is the ultimate target for evaluating an optical remote sensing system. This paper introduces the concept and physical intension of resolution, and educes the concept of optical cutoff frequency and image smearing from the diffraction resolution of diffraction-limited incoherent imaging. To evaluate the image quality of sampling imaging system, the IQF (Image Quality Factor) λF/P is used to perform the sampling extension of CCD. This paper discusses the relation between optical remote sensor and SNR (signal to noise ratio) of the image. Taking advantage of image simulation function of ZEMAX software, the image of a space-based remote sensor with 9 m focal length and F number being 18 optical system is analyzed. The pixel size of the CCD is chosen to be 8.75μm and 13μm . The simulation result validates the influence of λF/P and SNR on image resolution. This result will instruct the choice of CCD optical remote sensor parameter.