Analysis and suppression of stray radiation are significant component to infrared detection optical system design. Stray radiation will add the noise of system, and reduce the system detection ability of system on target. The stray radiation sources of infrared detection system were analyzed in this paper, and the theory of stray radiation based on ray-tracing was introduced. Then, the thought of backward ray-tracing based on an infrared detection optical system was advanced. After the characteristics of key surfaces were analyzed, the absorbing membrane of mechanical surface was introduced to suppress the stray radiation. The analysis results meet the requirements of stray radiation suppression.