By introducing the popular equidistant projection theory, a non-similar stereo vision was explored, and the three-dimensional (3D) location model and depth precision model were established. The correctness of proposed models was verified through carring out the 3D location experiment with a 115°×90° infrared stereo vision system. From the experimental results, the targets in different depths and large-airspace scene were located successfully. The depth error increases smoothly with increasing target depth, and it reached 1.32 m in the depth of 30 m. The error variation of 3D location model matched well with the results of depth precision model, and the whole error was obviously less than that of similar stereo vision model. The advantages of the proposed model is that the 3D coordinates of space target can be obtained directly without correcting the non-similar distorted images, and it contributes to enriching and improving the theory of stereo vision, and will help to spread the application of non-similar imaging theory in the fields of large-airspace situation awareness, target detection and so on.