We analyzed the stray light source of system and drew a conclusion that non-image beam has great effect on system qualities and system ghost images caused by parallel windows should not be ignored. In view of the facts that traditional graphical construction has less pertinence to stray light and tracing different incidence angle rays is fatiguesome and more likely to omit some rays, we proposed a reverse ray-trace method based on the ray reversibility. According to the method, a dot-matrix source was set at the image plane. Each dot emitted rays to fully cover the system aperture. A detector surface, large enough to receive all possible rays from the source, was set at object plane. Using the method, non-image stray light was easy to be recognized. Outside and inside lens hoods with special demands were designed,and its performance was simulated with software.