This paper describes a new decomposition method of structural intensity on a flat plate exciting at around natural frequency to modal components of the intensity. This method is based on the modal vibration displacement expressed by natural frequencies and modes. It is firstly shown that the displacement on the plate exciting at around one natural frequency is determined by the real parts of the displacement of resonance and non-resonance modes and the only imaginary part of the resonance mode. Shear force and bending moment are also expressed as the displacement is. Then the modal component of the structural intensity can be deduced by applying them to the equation of the structural intensity. In order to verify the method, an example of numerical simulation is demonstrated. As a result, the intensity component of the resonant mode is zero because the resonant mode is the standing wave and the net transmitted power is zero. And the summation of all components of the intensity is agreed with the direct calculation result.