The distributing current is calculated on the infinit plane mattaric grattings for the TM waves. The matrix is larger, when the moment method is applied this structure. So, the moment method of this case is required large memory and long CPU times. Those boundary condition and the scattering formura are transformed into spectal domain. Taking account of the peridic structure, this formular is changed in a series form by using the Flouquet mode. By making a suitable basis function, this equation is expreseed matrix form. So the distributing current on the mattaric strip is able to caculate by using this equation. We calculate magnitude of the distributing current for varing these spaces, widthes and an angle of incident waves.