The invention discloses a 3D shape internal hole digging type lightweight method based on function representation, and belongs to the field of computer aided design. The method comprises the followingsteps: firstly, expressing and exploring effective shape optimization analytical calculation by utilizing a function, then designing a stress structure of a 3D model by constructing an energy function model under given external condition constraints, modeling an object mass center, standing stability, tumbler design and suspension problems, and giving out a corresponding discretization form; andfinally, respectively carrying out geometric optimization on the modeling problems to obtain the internal shape of the optimized object under a given constraint condition. According to the method, thedesign and optimization period of the hole structure is greatly shortened, and a theoretically optimal result can be given. According to the method, the internal cavities of the obtained model are smoother and are not limited by the number of the cavities, the object model has a lower centroid, more materials are saved, and the consumed time in the aspects of design and optimization is shorter.