A method of to hydrological sheet color image segmentation based on gradient and color information is proposed and applied to paper hydrology data digitization to deal with the hydrological sheet images taken by camera. Firstly, curves are obtained by making use of color feature in the CIE Lab color space. Then the image is processed in a block-by-block manner. The gradient operators in horizontal and vertical directions are performed to discriminate the target pixels on the grid lines roughly. Thirdly, the color information of those pixels is obtained and the threshold to segment the grid lines are set. After getting the grid lines, horizontal and verticalerosions are implemented and most of the noise is removed. Finally, the segmented curves and the grid lines are merged and the final segmentation is established. The experimental results on several hydrological sheet color images show that the proposed method can fulfill the goal of image segmentation effectively in a self-adaption way and alleviate the effect of uneven illumination with good robustness and lower computational complexity.