Poly ether-carbonate diols were synthesized by ring-opening oligomerization of ethylene carbonate (EC) initiated/catalyzed by propylene glycol/[bmim]Cl-(SnCl2) system. It was shown that the oligomerization was accompanied with decarboxylation and chain cleavage. The stronger the lewis acidity of ionic liquid, the better the catalytic performances. The biogradability of the polyurethane foams which was prepared by poly ether-carbonate diols (or common polyether polyos ZS-4110) and diphenylmethane diisocyanate (MDI) was determined by soil burial and found to be influenced by the content of carbonate unit, molecular weights and the hydroxyl value of polyols respectively. Poly ether-carbonate diols can reduce the amount of MDI in synthesis of polyurethane foams.