The characteristic of overall structure for CMOS image sensor has been studied in this research. A three-dimensional solid model of CMOS image sensor based on finite element ANSYS software is developed to predict the thermo-induced strain and the stress induced by moisture absorption. The predicted thermal-induced displacements were found to be very good agreement with the Moiré interferometer experimental in-plane deformation. The developed finite element 3D model, therefore, is applied to simulate the mechanism of thermal and hygroscopic stresses based on JEDEC pre-condition standard JESD22-A120. A series of comprehensive parametric studies were conducted in this research. The design rules for thermal optimization of CMOS image senor are summarized.