The accuracy of crop rows line extraction is the key to the automatic navigation of agricultural machinery. In the paper, an improved algorithm is proposed to solve the problem of poor connectivity, single pixel and redundant pixels. Firstly, image pre-processing operations is used in order to obtain a binary image, then the binary image is thinned. In the refinement process, the connectivity of the skeleton is maintained by the introduction of Euclidean distance. Experimental results show that the proposed method has good adaptability to the row crop, and the skeleton lines that are extracted is more accurate. Compared with the traditional algorithms, the error of the navigation line is relatively small by using this algorithm, which could meet the needs of the practical application.