Cassegrain system is a typical coaxial reflection system,which has the characteristics of long focal length,large aperture and wide reflection waveband.However,the structure of Cassegrain system determines that it is seriously affected by stray radiation.In this paper,the stray radiation characteristics of Cassegrin system are studied and discussed.At first,the source of stray radiation of Cassegrin system is pointed out,and the optical machine model of the system is established in TracePro,which is a software of stray light analysis.Then the influence of external and internal stray radiation on the system is analyzed and the point source transmittance of the system is obtained,the stray radiation suppression level of the system is evaluated according to this transmittance.Finally,the baffles and other protection measures are designed for system′s stray radiation.