The absolute radiation calibration and long-term stability monitoring of the optical remote sensor can be realized by the ratioing radiation on-board calibrator, in which the diffuser illuminated by the sun is used as the reference light source, and the on-orbit degradation of the solar diffuser is corrected by the ratioing radiometer(RRM). The radiation response characteristics of the RRM is one of the main factors affecting the accuracy of the on-orbit calibration. The radiation response characteristics of the RRM is evaluated. The absolute responsivity is obtained, and the response nonlinearity and response instability are measured. The results show that the uncertainty of absolute response calibration is better than 2.88%, the nonlinearity is better than 0.93%, and the instability is better than 0.52%, which satisfies the requirements of on-orbit calibration applications.