The farm machinery vision navigation line extraction algorithm is influenced by the external environment, suitability and stability. An algorithm to extract the line for vision navigation based on dark channel is presented. Getting the gray image from the color image using dark channel, then obtaining the two values grayscale and filtering it using morphological method and Otsu method, and using the vertical projection method to extract the interested navigation region, next determining the navigation point in the region of interest. The navigation line location is extracted by the least squares fitting. The experimental results show that this method can be applied to different farmlands and road scenes. Compared with the traditional algorithm, the precision can meet the requirements of navigation line, and this method has faster speed. Besides, this method has wider applicability.