Abstract: When the installing height of camera was different or when the traffic running in the rough fields, there would be more than one crop lines exist in camera, in practical applications. An image algorithm which could determine all orientation lines of the targets in a crop image was proposed. The image algorithm eliminated the malpractice which need determining the number of orientation lines before extract navigation routes in tradition algorithm. The target regions were obtained by analyzing horizontal scan lines in the crop image, and then the improved Hough transformation was used to extract orientation lines. The average time required for a 720×480 pixels color image was 258 ms and the recognition rate reached 98%. The algorithm is availability in accurately detecting the orientation lines under different weathers.