Abstract: A hybrid technique is presented for analysis of electromagnetic scattering by electrically large bodies with deep cavities. Based on Domain Decomposition Method (DDM), the original deep cavity is divided into several small subdomains. By applying equivalence principle in combination with PO and PTD, the boundary Integral Equation (BIE) on the opening of the first subdomain is established. The transmission conditions at the interfaces of the other subdomains are applied to couple the fields within them. In each subdomain, the equivalent functional is deduced, and the edge-based FEM is applied to analyze the variational problem. It is shown that the hybrid technique has some advantages over other methods in regard to accuracy and saving computer memory units.