Abstract: The imaging quality can be easily degraded by stray light in some space imaging optical systems, so measures are taken to handle it. An optomechanical model of conformal optical system was established in stray light analysis software. And we tried to find out the systems critical surfaces in collecting out of field stray light by backwards ray tracing method. There were three baffles used in this system to block stray lights, and the simulation result proved the blocking effect of the baffles.