Nowadays, modelling and computer simulation are used in structure design to reduce the use of experimental investigations and laboratory tests required in a real layout structure. Using the potential-flow theory, the hydrodynamic pressure deduced from sea wave's propagation has been computed based on the non linear theory of Stocks. The extension to the floating breakwater behaviour due to such excitations is indicated in this paper. Analytical expressions for functional performance variables of wave reflection by vertical breakwater, and stress analysis of the floating breakwater have been obtained, yielding to the optimisation of its geometrical shape. These expressions have been numerically verified to demonstrate the capability of this analytical model.