Detecting the targets in near space will play a very important role in the future wars. A design scheme for detecting the target vehicles in near space by using a ground-based passive optical detection system is proposed. The spectral characteristics of the target vehicles in near space are analyzed in detail. The necessity of using multispectral means to detect the target vehicles is indicated for the system. The structure of the detection system is given. The design specifications of the detection system are analyzed in both the focal length of the optical system and the contrast. It is assumed that the diameter of a target is 20 m and the sun angle is 15°. When the optical system has its focal length of 280 mm, the contrast between the target and the background is 0.33. It shows theoretically that this system scheme is effective and feasible.