In the outdoor environment, mechanical equipments often inevitably touch and destroy overhead lines due to long mechanical arm or negligence, error judgment and sight restriction of operators. To avoid these damage accidents, a close distance warning system is proposed in this paper. Two cameras installed on a voltage pole are responsible for real time collecting images of environment. By means of distortion correction and foreground object detection, the two dimension coordinates of target object in the images are firstly computed. And then, by utilizing the mapping relation between two dimension coordinate of target object in the image and three dimensional coordinate of mapping point in the calibration panel in perspective projection model, both the three dimensional coordinate of mapping point and the distance between two cameras are obtained. Besides, the cameras are connected with the corresponding mapping point for making up two space lines, while they are intersected in the target object. Finally, the distance between target object and overhead lines can be obtained. When the distance is less than safe distance, the warning is sent out. Simulation experiments show that the proposed system can attain better accuracy and higher real time performance.