Recently infrared signature simulation has been in a state of great interest. Although various models have been developed to generate synthetic image of infrared scenes, little work has been done to create high fidelity infrared image of bridge. In this paper a realistic model for infrared image synthesis of bridge based on its thermal energy transmission is proposed to generate the infrared image of bridge at different time. Our new IR image synthesis model of bridge accounts for meteorological, environmental, material and artificial factors. Then an energy equilibrium equation is built based on the principle of heat transfer and infrared physics. And a finite difference method is adopted to solve the equations. Finally we get the radiance distribution of target surface. To get high fidelity, the effect of atmosphere is added using LOWTRAN model. The value of attenuation is pre-computed and stored in our database. We also pre-generate infrared texture and depth attenuated image from visible image. Infrared images of bridge from different viewpoints at different time can be rendered. Our results of simulation show that the model is robust and feasible.