A novel dynamic photoresponse model for complementary metal-oxide-semiconductor (CMOS) image sensors with pinned photodiode (PPD) structures is proposed. The PPD is regarded as the bonding structure of the two p-n junctions. The transient current equation of the two junctions is calculated by the current-voltage formula of the p-n junction, and the photoresponse curve of the PPD is calculated and drawn by the numerical solution. Simulation results show that the dynamic model successfully restores the entire process of the electron accumulation in the PPD. The difference between the full well capacity (FWC) values which were calculated by the proposed model and the simulation results is less than 5%, which is much smaller than the error of 40% for the traditional model.