In this paper, we propose a method to improve the problem that the assistant lane marks caused by pulse. We also define a method to distinguish the assistant lane marks' error rate objectively. To improve the problem, we mainly use the Sobel edge detection to replace the Canny edge detection. Also, we make use of the Gaussian filter to filter noise. Finally, we improve the ellipse ROI size in tracking part and the performance of the FPS (frame per second) from 32 to 39. In the past, we distinguished the assistant lane marks' error rate very subjectively. To avoid judging subjectively, we propose an objective method to define the assistant lane marks' error rate as a standard. We use the performance and the error rate to choose the ellipse ROI parameter.