Based on the simulation of infrared images of ships without any background, the principles and methods of computerized simulation of infrared images of ships in the ocean and atmosphere background were explored. The simulation is as follows: first, the ship target and the background, which consists of the atmosphere and sea surface, were treated separately to obtain their independent infrared images; then the two images were combined into one image of the ship in the background. A series of typical infrared images were computed by using the authors' calculating and displaying softwares.