An IR theoretical model of the ship was presented. The effect of the environment on the object, and the interaction between different parts of the object were investigated. The thermal model includes solar heating, sea/sky radiation, sea/air convection, the conduction between different parts of the ship and the surface radiation (which accounts for multiple diffuse reflections); the radiation and convection of the hold were also included. Based on the Monte Carlo method, the quasi random number was introduced to the calculation of radiant heat exchange between non diffuse gray surface of complex geometrical structure. The fluid, temperature field and IR emission of hot gas in the funnel were investigated and calculated. For a ship, the 3D surface geometry a target was defined, the temperature and IR emission field were calculated, and the simulated IR thermal image was presented.