In view of the fracture, tilt, deformation and other characteristics of railway freight car number, the traditional segmentation method has low segmentation accuracy. In this paper, a segmentation method based on improved bounding circle is proposed. Firstly, the adaptive run length algorithm is used to segment the double line train number based on the single line and double line arrangement of railway freight cars. In view of the characteristics of foreground processing of background pixels in run length algorithm, the run length algorithm is used to remove the break in advance, and then the encircling circle method is used for character segmentation. The experimental results show that, in the case of low image quality, it can achieve good segmentation accuracy, and is superior to the traditional algorithm in segmentation accuracy and robustness, which has high practical application value.