Waxy corn starch (WCS) was modified by amylosucrase (AS). The effect of starch elongation degree on the digestibility and physicochemical properties of modified waxy corn starch (WCS) was investigated. The results showed that under the given reaction condition, enzymatic reaction could be fitted by a logarithmic mathematical model. Compared with native starch, the modified WCSs expressed a continuous matrix structure, and the packing arrangement of crystalline converted from A-type into B-type. With transglycosylation rate (TR) increasing, an increased tendency of proportion of Fr I (DP＞30) was observed, whereas the contents of Fr III (DP＜13) was significantly decreased. In vitro test showed that the resistant starches (RS) were conspicuously enhanced in modified WCSs (53.1%≤RS content≤73.6%) compared to raw starch (RS content =0.8%). With the increased TR, the contents of RS in modified WCSs were increased at the beginning and attained the highest content (73.6%) when TR=88%, then RS content slowly declined.