For optimizing design of the High Dynamic Range Imaging system and evaluating its performance perfectly, the information theory is applied to the High Dynamic Range Imaging system, the High Dynamic Range Imaging system is considered as a communication system, and the image quality of High Dynamic Range Imaging system is evaluated according to the end-to-end mutual information. Introducing the influence of LCoS as a spatial light modulator to CMOS sampling imaging model, mathematical model of the High Dynamic Range Imaging system based on mutual information is established. According to the model, the factors, such as the ratio of LCoS pixel number to CMOS pixel number, aperture ratio of LCoS and CMOS pixel, relative displacement and relative rotation angle, which affect the mutual information, and the reasons why the system image quality decline are analyzed. According to computer simulation, the relationships between the ratio of LCoS pixel number to CMOS pixel number and the mutual information, aperture ratio of LCoS and CMOS pixel and the mutual information, relative displacement and the mutual information, relative rotation angle and the mutual information are demonstrated, and the influence of these factors on the mutual information is analyzed. The simulation results show that the best matching condition between LCoS array and CMOS array is that one LCoS pixel corresponds to one CMOS pixel with smaller CMOS pixel, higher aperture of LCoS and CMOS pixel, no relative displacement and no relative rotation.