In this study, we propose an on-board relative radiometric method based on a solar diffuser to correct the non-uniformity of the pixel response of the linear array CCD detector based on the imaging optical system of the push-room optical remote sensor. The proposed method uses laboratory integrating sphere calibration data as a reference standard to perform flat-field correction on the onboard calibration data, and the influences of the stray light in the field of view of the camera and the distribution of the bidirectional reflectance distribution function (BRDF) on the relative calibration results are eliminated; further, we obtain the relative calibration coefficients of each pixel, which can be applied to three different objects, i.e., the ocean, the Gobi desert, and the cloud. The results prove that the various vertical striping noises in the raw image can be effectively eliminated and that the image streaking metrics with respect to each scene is better than 0.0045 after relative calibration. Based on the solar diffuser, relative radiometric calibration for the linear array CCD detector in the large dynamic range can be realized, exhibiting considerable timeliness and calibration accuracy.