The invention provides a system for automatically righting a three-dimensional model of a product. In the system, the three-dimensional model of the product is subjected to triangular meshing, and a workpiece coordinate system of the three-dimensional model of the product is determined according to markup information in a two-dimensional dimension figure of the product; then the system generates a homogeneous unit matrix A2 of a mechanical coordinate system, calculates a translation homogeneous transformation matrix A1 of the workpiece coordinate system relative to the mechanical coordinate system according to coordinates of an original point of the workpiece coordinate system in the mechanical coordinate system, calculates a rotary homogeneous transformation matrix of the three-dimensional model of the product according to inverse matrixes of the homogeneous unit matrix A2 of the mechanical coordinate system and the translation homogeneous transformation matrix A1, and multiplies vertex coordinates of each triangle of the three-dimensional model of the product subjected to the meshing by the rotary homogeneous transformation matrix R, so as to obtain the vertex coordinates of each triangle in the mechanical coordinate system, after the three-dimensional model of the product is rightened. The invention also provides a method for automatically righting the three-dimensional model of the product.