Abstract: N, N-dimethyl oleamide propyl amine oxide was synthesized with raw materials such as oleic acid, dimethyl aminopropylamine and hydrogen peroxide. At 170℃ with sodium hydroxide (NaOH) as catalyst, oleic acid reacted with dimethyl aminopropylamine to form the intermediate, which in turn reacted at 55℃ with 30% hydrogen peroxide to produce N, N-dimethyl oleamide propyl amine oxide, gross percent conversion of which being 97%. A clear fracturing fluid was prepared with 1.5%-3% (mass ratio) of N, N-dimethyl oleamide propyl amine oxide and other additives, having viscosity in a range of 50-150 mPa·s after shearing for 1 hour at 170 s^-1 and 80℃. Clear fracturing fluid containing 3% (mass ratio) N, N-dimethyl oleamide propyl amine oxide had viscosity of 30 mPa·s after shearing for 1 hour at 170 s^-1 and 100℃. The N—O bonds in the molecules of N, N-dimethyl oleamide propyl amine oxide rendered it ability of strong viscosifying capacity. In laboratory experiment, clear fracturing fluids containing 2% N, N-dimethyl oleamide propyl amine oxide and 2% hydroxyl propyl guar gum, respectively, gave birth to permeability damage to artificial fractures of 13% and 90%, respectively, after flowing 10 PV of fracturing fluids, indicating that N, N-dimethyl oleamide propyl amine oxide is better than hydroxyl propyl guar gum in terms of reservoir protection. The clear fracturing fluid, when mixed with kerosene at 10:1 mass ratio, was allowed for the gel to break at 40℃ for 0.5 hour, and the viscosity of the fluid after gel breaking was 2.71 mPa·s, meaning that the gel was completely broken up.