With monocular vision sensor, we try to constitute a sensing system, which is able to realize localization, navigation and collision avoidance at the same time. We propose a novel sensing system with monocular vision sensor that is placed with a certain pitch angle in the front of the robot. The vision signal obtained by the vision sensor, which is partitioned into the upper and lower regions which are used in obstacle detection. In this paper, we will describe the hardware and system architecture of the sensing system. In detecting the obstacles, a search area is proposed for reducing calculation time. The lower region of the image is used as a reference area to reduce the effect of the reflected light in obstacle detection.