As for the optical measurement, the longer the focal length of collimator is, the less the measurement error is. However, the longer the focal length is, the more difficult the optical design is. It’s higher application value to design long focal length collimator with wide-view. The paper designs a collimator with 2000mm focal length, 4 degree field of view and its wavelength range is from 480nm to 750nm. The collimator is employed in the camera resolution detection system. It adopts the apochromatism three-piece-type structure and the secondary spectrum is corrected. The paper analyses the imaging quality of the optical system and the MTF curve is presented.