The maleic anhydride-modified corn starch was prepared from corn starch by sodium carbonate pretreatment in maleic anhydride molten system, and the composite material, maleic anhydride-modified corn starch/polylactic acid, was composited with polylactic acid. The 1HNMR test method for the degree of substitution of maleic anhydride-modified corn starch was established and optimized by one-way and response surface experiments using the degree of substitution as the response value; the micro-morphology, structural composition and thermal properties of maleic anhydride-modified corn starch were characterized by SEM, FTIR, XRD and DSC, and the mechanical properties and hydrophobic properties of the maleic anhydride-modified corn starch/polylactic acid were tested by using a universal testing machine and a water contact angle measuring instrument. mechanical and hydrophobic properties. The results showed that the optimal corn starch pretreatment process was as follows: sodium carbonate solution concentration of 0.97 mol/L, mixing time of 51.5 min, and starch mass of 2.5 g in 100 mL sodium carbonate solution, and the degree of substitution of maleic anhydride-modified corn starch (MA-ST-1) was 0.790, which was 91.7% higher than that of the modified starch prepared with the traditional technique (0.412) It was confirmed that the sodium carbonate pretreatment process effectively enhanced the conversion rate of esterification reaction. MA-ST-1 had smaller crystallinity (22.79%) and lower melting temperature (98.9 ℃), and the tensile strength and elongation at break of MA-ST-1/poly(lactic acid) were 47.771 ± 0.675 MPa and 13.728% ± 1.369%, respectively, and the water contact angle was 75.86° ± 1.19°. In the composite MA-ST-1/polylactic acid, the hydrolyzed product of maleic anhydride, butenedioic acid, acted as a bridge between corn starch and polylactic acid, which enhanced the mechanical properties and interfacial compatibility of the composite.