Abstract: The carboxymethyl maize starch was prepared using maize starch as a material, monochloroacetate ( MCA) as etherifying agent and sodium hydroxide ( Na OH) as catalyst by the mechanical activation-strengthened dry method.Single factor experiments and orthogonal array design methods were used to optimize the preparation conditions of carboxymethyl maize starch based on the degree of substitute ( DS) . The structure of the carboxymethyl maize starch were characterized by using fourier transform infrared spectroscopy ( FTIR) , X-ray diffraction ( XRD) and scanning electron microscope ( SEM) . The results showed that the optimum technology conditions were as follows: the mole ratio of starch and monochloroacetate was 1 ∶ 1, the mole ratio of starch and sodium hydroxide was 1 ∶ 1.25, ball-milling time was 90 min, ball-milling temperature was 60 ℃, stiring speed 380 r·min-1, tack media 500 m L, the DS of products 0.5086.The etherification reaction of maize starch had been confirmed further by FTIR, XRD, SEM.