Accurate and efficient vectorization are the foundation of engineering drawing understanding. The existing vectorization methods have three main shortages: (1) A line segment is fitted using a chain of medial axis points so that the computational complexity is high; (2) A lot of time-consuming searching and judging operations are needed to combine the separated segments caused by noise or intersections; (3) The capability of processing slant lines is much lower than that of processing vertical or horizontal lines. In this paper, the authors propose a seed segment based global line vectorization method, which vectorizes an entire line in one step so that the combining step is avoided. Furthermore, it processes the lines of any orientation in the same way. Both the performance evaluation and experimental results show that the performance of line vectorization is significantly improved using the proposed method.