The stray light of a space patrol is analyzed in this paper. The space patrol is used to observe the Earth in space. In the
paper the definitions of stray lights in the optical system are introduced and the stray lights are classified based on their
sources. After the analyzing the serious harm situations of the stray lights in the optical system is presented. Software
Tracepro is used in analysis of stray light. The model of the space patrol is established in the software and stray light
simulation and analysis of the space patrol are presented based on the evaluation criterion of maximum irradiance value.
Three different situations are discussed. First, sunlight directly irradiates onto the sensitive surface of the detector;
second, sunlight enters the system by the reflections of the space patrol’s body; and finally sunlight reflecting from the
moon’s surface irradiates onto the sensitive surface of detector by the reflection of the space patrol’s body. In each
situation, we respectively calculate different elevation angles in ranges between 15°~45° by the ray tracing method in the solar azimuth of 0° and 30°. Transmission paths of stray lights are obtained by ray tracing data in different
circumstances and the important surfaces of the system are found out. Finally, some corresponding stray light
suppression measures which can help to reduce harm of stray light are proposed.