Aiming at the practical problem of lacking quantitative guidance data on the performance of electro-optical system in complex environment， a method for evaluating the performance of electro-optical system based on the calculation of target and background optical characteristics was proposed. Considering the important influence of target and background optical characteristics， the calculation of target characteristics was introduced into the performance evaluation of electro-optical system. Based on the NvThermIP model that adopted the target task performance criterion， the calculation method of apparent contrast in the original model was modified. Using the radiation characteristic modeling technology， the calculation formula of apparent contrast based on radiance calculation was given， which could extend the applicability of apparent contrast calculation from infrared band to visible band. Thus， the NvThermIP model could be applied to electro-optical systems from infrared to visible wavelengths， and the accuracy of performance evaluation could be improved. Based on the measured data of the electro-optical system performance， the effectiveness of the method described was verified. The new method could achieve the goal of improving the accuracy of performance evaluation.