For assisting a binocular visual system of a small robot to recognize and locate the targets in middledistance, a pinhole lens installed in narrow space such as mechanical arms is designed. The stop is located infront-end of pinhole lens, and a piece of mirror is added behind the stop to turn the optical path to 90°, so the mainoptical path of the lens is parallel to the surface of the aperture and the lens is easy to be fixed and installed. The fo.cal length of the periscopic aperture lens is 12 mm. Optical characteristic analysis results of the final design showthat the requirements can be met when MTF is at 110 lp/mm space frequency. And it is a high resolution aperturelens matching 720 p high resolution sensor.