Abstract: In order to explore the best process of acid-heat preparation on sorghum resistant dextrin, the preparation process of sorghum starch was optimized by single factor and response surface experiment as well as its structural characterization was studied. The results showed that the optimum preparation process of sorghum resistant dextrin was hydrochloric acid addition of 21%, pyrolysis temperature of 188 ℃ and pyrolysis time of 84 min. Under this condition, the content of resistant dextrin was 86.71% and the chroma was 50.58. The prepared resistant dextrin showed an undulating and lamellar irregular structure. The original diffraction peaks were completely destroyed and a recrystallization peak was formed. The chemical groups did not change significantly and the peaks of each functional group were similar to the characteristic peaks of sorghum starch. The M_w of resistant dextrin after molecular degradation was 6.1×10³ g/mol. After the glycosidic bond cleavage and small molecule repolymerization reaction, the resistant dextrins have both α and β isomers, which indicated that the molecular properties was good. In addition, the results of simulated in vitro digestion experiment showed that the content of resistant starch could reach 93.61%, which indicated that it had good anti-digestion characteristics. In conclusion, the resistant dextrin prepared by acid-heat method could reduce the molecular weight of sorghum resistant dextrin and improve the digestibility. It also provides a new theoretical guidance for the efficient preparation of sorghum resistant dextrin.