Abstract: Investigates thermodynamically the Pb-oxychlorides formed during urban refuse incineration/melting by way of high-temperature XRD and activity determination of such solid oxychlorides, including the binary phase diagram of PbO-PbCl2, the relative chemical potential of PbO and standard free energy of formation or Gibbs free energy of activation of intermediate compounds. A thermodynamical basis is thus provided for the formation and precipitation reaction of Pb-oxychlorides during melting. Furthermore, the stability function and ideal associated solution model are employed to discuss the effect of stability of liquid PbO-PbCl2 on the formation of complex ionic species. The results show that the stable intermediate compounds are PbCl2 · PbO, PbCl2 · 2PbO and PbCl2 · 4PbO.