A method for optimizing the tolerancing of a set of flexible parts subjected to forces. At the design phase, an optimum tolerancing for flexible parts is defined according to the assembly process plan and the desired functional requirements. The structural digital models are considered as parts to be assembled and composed of a plurality of assembly points, a plurality of structural points, and mathematical relations or mechanical stiffness, such as a non-null relative displacement of a structural/assembly point in relation to the other structural/assembly points in a single digital model, modify tensor in each structural/assembly point. From a mechanical point of view, these mathematical relations express the existence of an elastic recovery property between the points that make up the digital model. The issue of optimization is simplified by: the definition of influence factors; the simulation of parts deviating from the nominal by a distortion vector.