An algorithm for line segments detection in digital image was proposed to improve the computation and the robustness of the traditional algorithm. The image gradient is meaningful to detect the edge of structure in the image; therefore its module and direction are computed in the first step. According to the pseudo-sort result of the gradient module, the region-growing method is implemented to enlarge the pixels with the same direction, where the connected pixel region is considered as a candidate region of line segments. Finally, enclosing rectangle is used to describe and judge the candidate region by long axis and short axis of the rectangle, belong which the long axis that meets the requirement is the desired line segment. Based on MATLAB program, an experimental simulation was performed. Experimental results depicted that 108 line segments after 8.87s of computation were detected by the proposed algorithm; which saved 17% of computation time and also detected 16% line segments more than the traditional LSD algorithm. This algorithm can accurately and quickly detect line segments in many complex environments in the image.