The stray radiation suppression in Cassegrain family optical system is presented. The design method for ultra-short outer baffle with honeycomb structure is proposed. Meanwhile the constraint formulas for designing the geometries of primary baffle and secondary baffle are deduced when basing the characteristic and taking vignette into account. According to the ray trace simulated data, the point source transmittance values of the baffle are less than 10-10 when incident angles are larger than the rejection angle. The honeycomb-look front baffle guarantees a comparable performance of stray light suppression with traditional tube baffle, while reducing the size greatly.