The methods to solve Maxwell Equations have been researched and developed for almost 50 years. The finite element method now plays a dominant role in this field. But the spurious solutions always come up with the physical modes, though we developed many methods trying to eliminate them and find the edge element method. In this paper, the author analyzed the physical background and the numerical behavior of the spurious modes in conventional nodal finite element formulations, and give the direction of the numerical method to eliminate them. The first time, the author derive out the spurious source term which influence the quality of the physical modes, and counteracting this source using the new penalty term can improve the field profile of physical modes. We also give the numerical results of a rib waveguide and a directional coupler.