The hydroxyl-terminated copolyether PTHF-PPO was synthesized by oxonium ions generated on both ends of polytetrahydrofuran(PHTF) molecules, which reacted with the hydroxyl groups of polypropylene oxide（PPO）, using concentrated sulfuric acid as catalyst under the condition of heating. The copolyether was characterized by GPC, IR and NMR,and the effect of reaction conditions on the polymerization yield and molecular weight of the product was studied. The yield and the molecular weight of the copolyether increase first and then decrease with the increase of reaction temperature, the extension of reaction time, or the increase of the amount of catalyst. The results show that the reaction temperature of 120 ℃～130 ℃, reaction time of 4h, the catalyst content being 4% of polytetrahydrofuran mass were the most satisfactory. The liquid copolyether with low viscosity is convenient for pouring process at normal temperature, and can be used as a good raw material for the polyurethane industry.