The polymerization of tetrahydrofuran (THF) initiated by heteropolyacid H3PW12O40(PW12) in low concentration could be effectively promoted by propylene oxide(PO) . The polymerization conversion reached 50%～60% after a reaction time around 5 h . Wateror butylene glycol was used to controlthe molecular weightofthe productin the rangeof 1000～3000 . The polymerization started upon addition of PO and stopped with completeconsumption of PO,but it would start again when a new portion of PO was added. The average hydroxyl end-group functionality of polyether glycol is close to 2. The ratio of primary and secondary hydroxyl end groups is close to one,and the percentage of the hydroxyl group attached to PO moieties at the polymer chain-ends is higher than 50% of the total hydroxyl end-groups. All the obtained results inferred that THF polymerization promoted by PO proceeded quite similar to that promoted by ethylene oxide,i.e., PO was necessary in the initiation of THF polymerization to start the propagation of chains,and with the complete consumption of PO the propagating chains transformed into dormant species,which can be re-initiated by thd addition of a supplementary portion of PO.