Abstract: Provided is an STL file coupling method including: analyzing models of STL files to define surfaces of the models as to triangular pixels, and selecting triangles to be coupled among the triangular pixels; determining directionality of a first triangle of a first file and a second triangle of a second file in terms of a clockwise direction or a counterclockwise direction; calculating first and second normal vectors from the first and second triangles, respectively; calculating a cross angle between the first and second normal vectors; arranging the first and second triangles to face each other in parallel; calculating a first central point of the first triangle and a second central point of the second triangle to calculate a distance between the first and second central points; and moving the second triangle with respect to the first triangle by the calculated distance to couple the first triangle to the second triangle.