Abstract: The Monte-Carlo method is applied to calculate the stray light of an infrared optical system.The system's geometrics tructure and the physical kinds of its elements are standardized.Some relevant probability models are established and a ray tracing approach is employed which can speed the calculation effectively.On the basis of those,an universal computer program is developed,and the stray light of an infrared camera has been analyzed.

Key words: stray light, Monte-Carlo method, infrared optical system