Designers often want to analyze more and more sophisticated structures, thus leading to very large "nite element models (typically 10 00 000 degrees of freedom for a body car, for example). These models being too costly for the early stages of design and optimization can be reduced by a substructure analysis or a mesh simpli"cation of the components. A methodology is proposed in this paper for simplifying "nite triangular plate element models leading to a dramatic reduction in the number of degrees of freedom while preserving the dynamical properties of the initial system. In particular, the proposed method is developed for models composed of the plate element STIFF63 generated by the software ANSYS. The principle consists in determining the parameters (thickness, Young's modulus, density) of the triangular elements of a coarse model which replaces a large set of elements of the re"ned model. The simpli"ed mesh must satisfy one of two criteria. The "rst requires that the mass and sti!ness matrices of the simpli"ed model be as close as possible to the Guyan condensed matrices of the re"ned model on the reduced node set, whilst the second requires that the dynamical properties of the global structure be preserved. The application of these approaches is illustrated on two test structures using the gradient method to solve the resulting optimization problem. The second approach is shown to give the best results. Typically, the size of the models can be reduced by a factor of 20 whilst preserving the dynamical properties of the structure at low frequencies.