A binocular passive ranging system is developed. The key techniques of binocular ranging are analysed in detail. An improved algorithm of matching is proposed. By incorporating sketchy matching with accurate matching,and using parabola fitting, the matching position can be obtained quickly and accurately in the orde r of sub-pixel . The experiments on the ranging systems stability, repeatability and precision have done. The results show that the ranging relative2error is below 4% for a target at 10 km and the response time is less than 0. 5 s. The advantages of high accuracy, real2time make itwill be attractive in mobile target positioning.