The connection between the rectangular plat and the longitudinal vibration transducer always has a certain contact area in high-power applications.Thus the deformed nodal line of stripe vibration mode don′t coincide with the expected step edge positions.Using combination of the method of numerical calculation and finite element, the influence of the excitation area on the directivity pattern in (8,0) stripe mode flexural vibration is investigated. The result shows that, for the 180×120×5 mm (length×width×thickness) rectangular plate, the nodal lines deform gradually with the increasing of excitation area.The (8,0) modal resonance frequency increases.The directivity pattern becomes less sharply and the acoustic field directivity pattern along the y axis is sharper than that along the x axis.When the radius of the excitation area increases to 12 mm，the side lobe is obvious.The radius of the excitation area should not be greater than 8mm for the stepped plate.

finite element method; rectangular plate; excitation area; nodal line; directivity pattern