Abstract: To verify and increase the resonant frequency of the platform of a tri-axial vibration test system, and furthermore, to extend the frequency range of the system, the mode of the work table under the free state is simulated using the FEM software, and the simulation results and the tri-axial test results are compared. It is shown that the differences of the bending frequency of the opposite angles or sides are less than 10%. And the result can provide a technical support for the future design.