In order to solve the injury of optical sight to shooters, which is produced by recoil for using artillery or firearms, and the usage problems of shooters’ eye mask, headband and gas mask, the ocular with long exit pupil distance has been designed based on optical sighting system. The optical properties and aberration characteristics of ocular with long exit pupil distance has been analyzed, the structural style with positive-positive-negative three lens groups has been put forward. According to the aberration theory and the isoplanatic image formation principle, the focal power assignment expression has been deduced by adopting analytical method. By using of optical design software ZEMAX, the ocular with long exit pupil distance has been designed, the focal length of system is 20mm, the exit pupil diameter is 4mm, the field angle is 40°, the distance of exit pupil is 41mm, and the relative eye relief is greater than 2. The design results show if this method has been adopted, the transfer functions of each field are all greater than 0.15 when the ocular with long exit pupil distance locates on 45lp/mm, which can meet the use requirements of visual optical instruments.