Abstract: Oil-soluble polyether (OSP) was prepared by the copolymerization of propylene oxide and butylene oxide using KOH as a catalyst. The viscosity grades of the prepared oil-soluble polyether are OSP-18，OSP-46，OSP-150, respectively. The structures of the products were defined by means of infrared spectroscopy (IR), nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The anti-oxidation performance of OSPs were investigated by rotary oxygen bomb test method (ROBT). The results indicate that the oil-soluble polyether is poor in anti-oxidation with short induction period. However, the performance of the oil-soluble polyether is greatly improved by addition of the composite antioxidant, composed of α-aniline (AOA-4) and carbamate (AOL-1). The ROBT can reach to 1200 minutes. The performance of this composite antioxidant makes OSP the best application in different formulations.