The main optical system of multi-band co-caliber infrared system is designed by using a Cassegrain telescope whose primary mirror (PM) and secondary mirror (SM) are aspherical form, and the structure of which is using total reflection system for the former level, the refractive lens group for the stage. After the target radiation to reach the primary mirror, reflecting onto the secondary mirror, and on top of toggling the spectral radiometric flux , respectively, which is reflected by different spectrum region, transmit to infrared focal plane array (IR FPA) for each other imaging detector. Then, photoelectric converse those information which were received by IRFPA. The output signal of detectors are processed and displayed by Read-Out Integrated Circuit (ROIC). We are confirming the image quality of different bands during system model optimization design. According to the specification of design system, establishing the measurement program of quantitative study. The results experimental measurement shows that the optimized design of the optical system has good validity.