It has great significance to study the relationship between degree of substitution (DS) and physicochemical properties for improving the OSA-starch's performance. A series of OSA-starch samples with different DS were prepared from waxy corn starch and OSA, the preparation conditions were discussed, and the change of characteristic absorption peak with DS was determined by infrared rays. The effect of DS on the OSA-starch's emulsifying property encapsulating property was investigated. The results showed that the emulsifying capacity and emulsion stability increased firstly and then decreased with the increasing of DS, while the encapsulating rate increased all the time, but both of them lower than that of the imported product. The structure of the home-made and imported products was further analyzed by using XRD and DSC technology, the results showed that the internal structure of starch is one of the important factors which may affect the OSA-starch's emulsion and encapsulating properties.