Abstract: With the continuous deepening of human space exploration, the automatic on-orbit capture and maintenance of faulty spacecraft has become one of the urgent needs for the development of space technology. The prerequisite for capturing the target spacecraft is to obtain the relative position and attitude between the two spacecraft online. Among many measurement methods, vision has become one of the main methods for short-distance measurement in space. This paper takes the spacecraft docking ring of unknown size as the measurement target, and proposes a pose solution method that combines the information of the binocular structure and the geometric shape of the three-dimensional target. The simulation experiment simulates the approaching process of the tracking spacecraft to the target spacecraft, which proves the effectiveness of the algorithm.