In this paper, we use two visible laser points as the measuring ruler for automatically adjusting measurement. It is a breakthrough compared with using double CCD cameras or the measuring method of setting up reference at measuring points. By using a single image, we can realize the non-contact distance measurement. The measuring principle is to produce two bright projection spots on the measuring surface with two parallel lasers projectors. As a result, the pixel value between the spots will change in accordance with the shooting distance. As long as the pixel value between the two bright spots in the image frame can be identified, distance measurement can be obtained for detection and obstacle avoidance for mobile robots by using a single camera image.