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Objective The effects that stray light has on satellite-borne infrared optical systems are embodied in two perspectives, one is degrading the quality of imaging, and the other is decreasing the precision of calibration. Satellite-borne infrared optical systems are situated in the environment of extraneous atmosphere where stray light is simply formed at specific operating position relative to celestials such as the Sun and the Moon. Owing to this, the payload’s imaging capability and the precision of calibration rely vitally on the evaluation of stray light. The Visible and Infra-Red Radiometer (VIRR) which embarks FY-3A/B/C satellites has been operating in orbit for more than ten years, during which the massive quantity of data acquired are significant for the study of climate change. The long period of payload’s consistent operation covered various circumstances of illumination. By evaluating the variation of payload’s response in long time sequence, the changing trend of payload’s on-orbit performance can be obtained, which is of great significance for the recalibration of historical data. Method The imaging optical system of the VIRR is modeled and simulated by means of TracePro, which yields the point source transmittance (PST) curves of different spectral bands in pitch, scan and yaw dimension, respectively. PST is one of the widely adopted indicators for the characterization of an optical system’s response to stray light. It is defined as the radiance of the detector aroused by an off-axis point source, and then normalized to the entrance pupil radiance when the point source is on axis. The experimental stray light measurement of the backup of the on-orbit instrument is conducted as well. Based on the experimental results, a comparative analysis between simulated result and actual measurement is achieved qualitatively. Possible incident angles for which the instrument is susceptible to stray light are found by studying the PST curves. A shield is later mounted on the instrument to demonstrate the effectiveness of stray light suppression method. In order to evaluate the on-orbit performance of VIRR under stray light influence, the simulation and analysis of orbital parameters, especially the solar irradiance, are performed as well. Taking into consideration of the mutual effects of payloads, the illumination situation during satellite crossing terminator is simulated, and the path through which solar contamination influences the instrument both externally and internally is found. Result The PST curves of pitch, scan and yaw dimension of VIRR reveal the geometric profile of the instrument. The peaks of pitch and scan dimension appear at off-axial angle of 10°, which is consistent with simulation results. Likewise there is a peak at large off-axial angle (~75°) in the pitch dimension, which corresponds to stray light incident from the motor side. The yaw dimension PST is 2~3 magnitudes lower than that of pitch and scan dimension within the range of ±20°. This is due to the blockage of the motor housing. Preliminary results of magnitude of stray light are also obtained. The transmitting path of stray light is predicted by simulation results and later verified by on-orbit data. Conclusion This work can provide reference to the design of similar payloads with regards to suppressing stray light and preventing sun contamination. The results yielded can fundamentally support the recalibration of historical remote sensing data as well.