Abstract: In order to achieve accurate detection of the outdoor infrared ranging system in a limited confined space, the volume of the optical system needed to be compressed on the basis of not affecting the detection results, and a set of foldback optical paths with a total optical length of 4 m and a maximum mirror of 12.8 cm was designed using a two-dimensional biplane reflector system. The foldback optical path was divided into 2×(n+1) sections with n planar mirrors, and the number of mirrors and the optical diameter were optimized using the Global Search algorithm, so that each detection ray could irradiate the detected object and be successfully folded back to the detector. After meeting the detection requirements, the theoretical verification analysis was carried out by using the signal wave principle to avoid the detection errors caused by the optical range loss. Finally, by analyzing the simulation results of stray light of the system in a confined space, the stray light suppression of the system was carried out, and the experiments were compared with the detection results of the original path to verify the correctness and accuracy of the design.