Fully optimized calculation and frequency analysis of 209 polybrominated diphenyl sulfide (PBDS) were carried out by using a DFT method at the B3LYP/6-31G* level and their thermodynamic parameters were obtained. The isodemic reactions were designed to calculate standard enthalpy of formation (Δ_fH⁽) and standard free energy of formation (Δ_fG⁽) of PBDS congeners. The relationships of these thermodynamic parameters with the number and the position of Br atom substitution (N_PBS) was established, finding that there exists high correlation between entropy (S⁽), standard enthalpy of formation (Δ_fH⁽) and standard free energy of formation (Δ_fG⁽) with N_PBS (R²≥0.993). The stability of PBDS congeners was theoretically proposed based on the relative magnitude of their Δ_fG⁽. The values of C_p,m were calculated by using statistical thermodynamics calculation program at the temperatures from 200 to 1000 K based on Gaussian 03 output files, and a relative equation between C_p,m and temperature was obtained by the least square method, finding that C_p,m has a very good relationship with T, T^－1 and T^－2 (R²＝1.000).

Key words: polybrominated diphenyl sulfide, density functional theory (DFT), method of position of Br atom substitution, thermodynamic property, relative stability