The active imaging system has shown great potential in harsh environmental conditions, but the imaging quality of the system under certain conditions is difficult to be assessed. Therefore, we performed accurate physical modeling and imaging simulations of the active imaging system. In this paper, we analyze the signal transmission and degradation mechanism of active imaging by considering the global radiation and scattering elements of the imaging profile. Then, a full-chain imaging pixel equation is established to characterize the information conversion process, and global radiation elements such as backscattering, ambient radiation, and atmospheric turbulence are coupled into the imaging conversion model for higher accuracy. Furthermore, various design parameters and environmental parameters are coupled with the imaging model and a 3D digital prototype of the active laser imaging system is completed. The degradation of imaging contrast and range caused by visibility, atmospheric turbulence, aerosol type, and solar zenith angle is quantitatively evaluated. This research can provide useful support for the simulation analysis and performance prediction of active imaging systems.