To accurately detect the baseline of crop row in real time, a navigation line extraction method that combine boundary detection and scan-filter (BDSF) was proposed. Firstly, the binary image that contained the crop row information was obtained correctly after image preprocessing, including gray scale processing which adopted the G-R color feather method, and binary processing which use the OSTU method. Secondly, the position of crop row was calculated by vertical projection of the image top and bottom. Thirdly, numbers of rectangle bars of width equity was used to scan the effective information of image points in the rectangle boxes. Finally, the navigation line was extracted according to the scanning results. The experimental results showed that, the BDSF algorithm could quickly and accurately extract the navigation line. The time consumption for single image of 640 pixels×480 pixels was about 67ms. Compared with Hough transform and LSM algorithm, the designed algorithm had the advantages of high speed and good robustness.