The invention is a computer-implemented method for defining a supporting structure (2) for a three-dimensional object (1) to be produced through a stereolithography process, comprising the following operations: defining a first surface (3) to be supported of the three-dimensional object (1) and a second surface (4) facing the first surface (3); defining elongated supporting elements (5) between the surfaces (3, 4); defining pairs of supporting elements (5); for each pair of supporting elements (5), defining an elongated reinforcing element (6) connecting the two supporting elements (5) of the pair. The definition of the pairs of supporting elements (5) comprises the following operations: defining a reference point (7) of each supporting element (5); defining a connected acyclic graph (8) having as vertices the reference points (7); for each edge (9) of the graph, defining one pair of supporting elements comprising the two supporting elements (5) corresponding to the ends of the edge (9). The definition of the
