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According to the theory of Fourier Optics, an optical remote sensing imaging system is an optical diffraction-limited system and a low-pass filter. CCD or CMOS imaging sensors are low-pass filters as well. Thus, when the optical information of an object or a scene with abundant high-frequency components passes through the remote sensing optical imaging system, the profuse middle-frequency information is attenuated and the rich high-frequency information is lost, which will blur the captured remote sensing images. To solve this problem of the imaging system in the remote sensing satellite, an analog on-line compensating method of the Modulation Transfer Function (MTF) in the imaging system is proposed in this paper. The established method was realized by a hardware analog circuit placed before the A/D converter, which is composed of adjustable low-pass filters with a calculated value of quality factor Q. All the theory analysis, experiment results and application in the remote sensing imaging system of the satellite showed that the proposed method and the realized compensating circuit are capable of improving the MTF of imaging systems and enhancing the middle frequency of blurred video images.