Starch octanoate (St-C8) with different degree of substitution (DS) were synthesized by corn starch and octanoyl chloride in organic solvent. The structure of St-C8 was identified by infrared spectrum. Moreover, St-C8 was used as the emulsifier of soybean oil and water system. The effect of DS, emulsifier concentration and the proportion of oil phase and water phase (VO/W) on the emulsibility and emulsified stability of emulsion were also investigated in detail. The result indicated that St-C8 exhibited the best emulsibility and emulsified stability when the DS and concentration are 0.37 and 7%, respectively. Furthermore, the emulsion exhibited the best emulsibility and emulsified stability when the VO/W is 4/6 and 2/8, respectively.