The ring-closing reaction of chloride polyether polyol was calculated by Gaussian03 software. The Density Function Theory (DFT) method were employed to study the geometry structures of chloride polyether polyol and the product was obtained on the base of B3LYP/6-31G+ model in this paper. The transitional states (Ts1, Ts2) during the ring-closing process were found by TS method and the energy changing of the system was proved by IRC calculation. Results showed that the ring-closing of chloride polyether polyol had two transition states: hydrogen transferring and the formation of new carbon-oxygen bond. The total energy of reactants was -1459.99627a.u and product is -1460.31170 a.u. The energy of the system was reduced by 175.47621kJ/mol. The ring-closing of chloride polyether polyol was exothermic and stable in thermodynamics.