An optical system suitable for a new type of airborne multispectral common-aperture targeting pod is designed by adopting a folded off-axis three mirror telescope as the common optical path component. The optical system is characterized by miniaturization, high transmittance, multispectral, long focal length, and low difficulty of installation and adjustment. The designed multispectral common-aperture optical system has an effective optical aperture of 220 mm, a near-infrared focal length of 1100 mm, a short-wave infrared focal length of 1200 mm, and a medium-wave infrared focal length of 880 mm. It can be integrated as a transmitting and receiving antenna with a laser sensor, which shares the same aperture and fast steering mirror with other imaging sensors. The system is mounted on a typical airborne spherical electro-optical pod platform with a diameter of 500 mm. The optical design analysis and results indicate that the image quality of the optical design has reached the diffraction limit. All indicators and parameters meet the technical requirements.