1. A curved surface importing method, the method comprising steps of: importing character strings of graphic parameters and graphic attributes of graphs from an initial graphic exchange specification (IGES) document stored in a storage system; analyzing the character strings of each of the graphs to generate a graphic model; converting the graphic model to a plurality of free-form curves and a free-form curved surface, connecting each of the free-form curves to generate a closed boundary curve, and cutting out a contour surface from the free-form curved surface according to the closed boundary curve; meshing the contour surface using a plurality of triangles, and determining an approximate poly-line of a boundary of the contour surface; and displaying the plurality of triangles and the approximate poly-line on a display screen.