With the development of space technology, space manipulator has become an important tool for space maintenance and on orbit service. In order to capture the target satellite automatically, the space manipulator should measure the relative position and attitude between the end of the manipulator and the target continuously as the input of the closed loop control of the manipulator. This paper focuses on the automatic capture of the target spacecraft by the space manipulator, and researches the relative position measurement method based on the structure light, using the docking rings which are commonly exist on space spacecraft as the capture object. It proposes a position measurement method which meets the requirement of the space manipulator for automatic capture of large scale docking ring target at a close range based on multi-line structure light. First, it selects the combination of the line feature and the point feature through the analysis of the captured object based on line structure light measurement system. It proposed a method of target recognition and feature extraction in structured light image under complex background based on the selected target characteristics. This method is used to extract laser stripe region by region growing; the object stripe is identified by the constraint of the shape constraint of the laser stripe and the geometric relationship between the light stripes and then fits the line. A pose solution algorithm for single set of structured light is proposed based on the target characteristics. It calculate the circular plane normal vector by plane fitting to get three dimensional coordinates of light stripe feature points, using the intermediate coordinate system to solve the circular center coordinates. Based on the solution of the single set of structure light system, double sets can provide redundant information which is used to improve the accuracy of measurement. Up to the measurement method, we established an experiment system based on structure light, and developed a visual measurement software. The posture measurement experiment is carried out and the accuracy test is completed in several experimental scenes. It shoes that the proposed method is environmental adaptable and with high accuracy through the experiment results. Above all, it proposed a method based on structure-light that is oriented to capture the space manipulator to the docking ring automatically. In the condition that the docking ring can only be partially imaging in the measurement camera, the high precision measurement of the relative position between the manipulator and the docking ring can be realized, and it has a good adaptation to the environment change. The method has been applied in practical engineering projects.