The vibration and suppression of the finite L-shaped plate with square steel is studied by using wave method. The finite rib-stiffened L-shaped plate is modeled as the coupling systems between the flexural and in-plane motion for the plate and the flexural, torsional and axis motions for the square steel. The vibration response at any position of the coupling structure can be obtained by wave method. Numerical results show that comparing to finite element method (FEM), not only the low frequency but also the medium-high frequency vibration response of the finite plate with square steel can be effectively calculated by wave method. The suppression effect can be increased with the torsional stiffness of the square steel as the steel is located at the junction of the L-shaped plate. And optimal suppression effect can be obtained as the steel is located at two third the length of the source plate or near the junction on the received plate.