In this paper, we design a modified two-grid method (MTGM) for the Maxwell’s system by adding one correction on the coarse mesh, called postprocessing technique, to the classical two-grid method (TGM), which makes MTGM run smoothing for the edge element like Lagrange elements. The considered Maxwell’s system describes the non-local dispersion model for light interaction with metallic nanostructures. The main contributions of this paper have three parts. Firstly, we give the integral expansion formulas in order to set up supercloseness in the first step of MTGM. Secondly, we take a group of superconvergent solutions on the coarse mesh into the second step as the correction values. Such an algorithm overcomes the difficulties that the edge element can not be applied to the numerical electromagnetic system by TGM directly. Thirdly, we employ the Crank-Nicolson fully discrete scheme to obtain a convergent rate O(τ2 +h+H2) by using the lowest mixed N´ed´elec − Raviart − Thomas finite element, where τ is the time mesh size, and H, h is the course mesh size and fine mesh size in space, respectively. In the end, we present two numerical examples to verify our algorithm, which demonstrates that the MTGM can save about 30% CPU time.