A well-conditioned coupled set of electric field integral equation (EFIE) and thin dielectric sheet (TDS) approximation surface integral equations for analyzing densely discretized composite structures with perfect electric conductor (PEC) and thin dielectric layer is proposed. Whereas TDS operator is well-posed, a EFIE operator is ill-posed when applied to densely discretized surfaces. This makes the coupled EFIE and TDS linear system ill-conditioned, and its iterative solution inefficient or even impossible. The proposed method regularizes the coupled set of EFIE-TDS using a Calderon multiplicative preconditioner (CMP) technique. The resulting linear system enables the efficient analysis of composite structures with PEC and thin dielectric layer. Numerical example validates the efficiency of the proposed method.