In this study， starches of three typical crystalline including corn starch (type A)， potato starch (type B) and pea starch (type C) were used as raw materials， and modified by compound-enzymes (branching enzyme， β-amylase) and ultrasonic-compound-enzymes strategies to explore the structures and digestive characteristics of the three kinds of typical crystal starches before and after modifications. The amylose content， branching density， molecular structure and crystal structure of the three kinds of starch before and after modifications were analyzed by means of iodine-blue method， nuclear magnetic resonance hydrogen spectrum， Fourier transformation infrared spectrum and X-ray diffraction， and the mechanisms of the effect after modification on the digestible properties of starches were further explored. After the compound-enzyme treatment， the results suggested decreased amylose content and the relative crystallinity， while the branching density and the degree of molecular order were increased. The hydrolysis index (HI) and glycemic index (GI) of slow digestion starch were significantly increased， and the changes of pea starch were the largest among the three kinds of starches. The above indexes were further improved after the application of ultrasound. The three kinds of starches were transformed into C+V structure with V structure as the main crystal after modifying by ultrasonic-compound-enzymes strategy. Conclusion: Among the three typical crystalline starches， pea starch was the most sensitive to modification by compound-enzymes strategy. The ultrasonic-compound-enzymes strategy can change the structure of starch more efficiently， thus improving its digestibility. The above researches could provide theoretical basis for developing processing technology of functional food with desirable GI.