By response surface analysis to optimize the preparation of OSA starch.The RSA tests show that: time of 3.5h,temperature of 48℃,pH of 9.3,the yield of RS4 up to 21.51%.The OSA starch did not destroy the basic structure of raw starch obviously,the damage caused by esterification in most large particles,a number of small particles through the ester linkage in the large particles,so that the particles tight with each other closely.Through the investigation of the resistant starch in yogurt fermentation to the proliferation of LA-5 and BB-12.It preliminary proves that the prepared resistant starch has no obvious effect on LA-50 proliferation.Nevertheless,it has obvious effect on the BB-12 proliferation.OSA starch and commercialization of resistant starch Hi-maize260 have similar effects,the bacterial viable numbers were up to 1.01×109 CFU/mL and 1.03×109 CFU/mL,there are about 7 times more tha the blank.