In the research, a star-shaped surfactant was synthesized through the chlorination reaction, alkylation reaction and sulfonation reaction of triethanolamine. The star-shaped surfactant synthesized is composed of three hydrophobic chains and three sulfonate hydrophilic groups. Study found that the surfactant has high surface activity with CMC of 4.93×10-5 mol/L and interfacial tension of 32.0 mN/m. At the same time, the effects of the star-shaped surfactant’s concentration and alkalinity (NaOH concentration) on the interfacial tension of the crude oil-water interface would be discussed. It’s indicated in the research that a small amount of star-shaped surfactant can effectively reduce the interfacial tension of crude oil-water interface. When the surfactant concentration was 0.1 g/L and NaOH concentration was 0.5 g/L, interfacial tension of crude oil-water system at 50 ℃ dropped to 1.1×10-4 mN/m, which suggested that the surfactant reached the ultra-low interfacial tension, which can satisfy the requirement of surfactants for oil displacement. And the self-emulsification experiment indicated that the surfactant had excellent emulsification performance. When the surfactant concentration was 0.1 g/L, the crude oil would be turned into O/W emulsion with particle size of 5 ~ 20 μm.