Owing to their extremely high toxicity in the environment, the dioxins have been attracting social, technical and scientific attention in recent years. The authors theoretically had predicted the thermodynamics properties of all the dioxins via quantum chemistry and statistical thermodynamics and elucidated the generation-decomposition behavior of dioxins in the equilibrium calculation of C-H-O-Cl system. In actual combustion processes, it is said that metallic compounds have much influence on the dioxins behavior. The aim of this study is to reveal the roles of metallic compounds the generation-decomposition behavior of dioxins is revealed from the viewpoints of quantum chemistry. Especially, the catalytic effect of copper has been investigated for the reaction, 2HCl(g)→H2(g)+Cl2(g) and for the etherification reaction from precursors, which is Phenol(g) here, to dioxins. The catalytic role of Cu is shown to have much influence on the generation -decomposition of dioxins.