Abstract: This paper presented a method to extract feature lines from the triangular mesh based on the MorseSmale (MS) complex. Firstly, the MS complex is constructed with curvedness as the indicator function. Critical points and decending/ascending arcs of the complex compose the initial group of feature lines. Then the significance factors of the feature lines are defined and less important features are removed by a simplification process. The computational results show that this method can automatically and efficiently extract the connected feature lines.