Abstract: The SNR is one of the primary parameters in optical sensor system,which can be used to reflect radiation performance of remote sensor.The orbit model of the remote sensing satellite was built,then the solar angle and observer angle,which were used to describe the relative position of the sun,the satellite and objects,were input into the air transmission software MODTRAN,the spectral radiance calibration was output by this model,and the real time SNR of TDICCD camera was completed.By the proposed method,dynamic SNR at any time and for any observation objects can be calculated,which will help to estimate whether the energy is enough for observation.The result is used to change the level of TDICCD to make the image quality best.