Abstract: The calculation speed of cross-sectional information is one of the key links affecting the efficiency of slicing in Rapid Prototyping & Manufacturing. In this paper, the position relationship between a facet and a slicing plane is analyzed, and a highly rapid and efficient algorithm for calculating cross-sectional information is proposed, which also can be used for imperfect STL model. The identification of inner and outer contours needed for radius compensation can be omitted. Practical applications show that it can greatly improve the efficiency of slicing.