The thermodynamic properties of 136 polychlorinated phenarsazines (PCPAZs) have been calculated by density functional theory at the B3LYP/6-31G* level. Then, isodesmic reactions are designed to calculate Delta H-f degrees and Delta(f)G degrees of PCPAZs. The relations of these thermodynamic parameters with the number and position of Cl atom substitution (N-PCS) are discussed and a relative stability order of PCPAZs is theoretically proposed according to the relative magnitude of their Delta(f)G degrees In addition, the values of molar heat capacities at constant pressure from 200 to 1000 K for PCPAZs are calculated, and the temperature dependence relations of this parameter are obtained using the least-squares method.