Vacuum drying method was chosen to preparing sweet potato granules.The effects of vacuum drying temperature,leaching of calcium concentration,cooking time and concentration of the added emulsifier on the free starch content of sweet potato granules was discussed.The optimal conditions were as followed through orthogonal experiment: the vacuum drying temperature 40℃,leaching of calcium concentration 25 mg/L,concentration of added emulsifier 0.2%,cooking time 12 min(the quality of sweet potato granules are best),and the free starch content of sweet potato granules is 21.89%.