Abstract: Waxy maize starch was selected as the material, acid pretreatment before the acetylation was introduced in the preparation of the modified starch. The corresponding physicochemical properties of the modified starches, including the viscosity, transmittance and the swelling power were investigated, the structural changes of the modified starches were observed and analyzed by means of FT-IR and XRD. The results showed that acid pretreatment decreased the viscosity of the modified starch, the cold and hot paste stability of the paste was improved, the modified starch was of lower gelatinization temperature than corresponding acid-thinned starches but higher than acetylated starch, the retrogradation of modified starch was improved. After acid pretreatment, the transparency of the paste increased obviously, swelling power was decreased, low acid concentration had less influence on the freeze-thaw stability whereas high acid concentration decreased the freeze-thaw stability obviously, acid pretreatment had little influence on the crystalline and granular structure.