Abstract: Aiming at the needs of infrared (IR) searching and tracking system for target detection, a two-color infrared common aperture system was designed in order to improve the detection ability of optical system under complex environment. The working waveband of the system covered the medium-wave(3 m~5 m) and long-wave(8 m~12 m), the dual-band clear imaging was achieved by using dispersive Ritchey-Chrtien (RC) system, the overall focal length of the system was 400 mm, the relative aperture D/f was 1/2, and the full field of view was 2. In order to suppress the medium-wave thermal radiation stray light, the mid-wave infrared (MWIR) system achieved the secondary imaging, through rational calculation of IR material and focal power, the optical passive athermal design was achieved. The results indicate that the image quality is excellent under the working temperature of -40℃~+60℃, which can meet the using requirement of infrared searching and tracking system.