CMOS active pixel sensors (APS) suffer from serious dark-current degradation when they are exposed in radiation environment. Considering the general situation that there are multiple kinds of energetic particles in radiation environment, a dark-current estimation method for pixel sensors due to mixed radiation particles is proposed in this paper. Based on the radiation effects induced by particles of all kinds, the dark-current amplitudes distribution among the pixels can be predicted through probabilistic analysis. Validation is implemented upon the radiation dark-image data of CMOS APS devices, which shows that the predicted dark-current distribution matches very well with the experimental data, and the difference is no more than 15%.