Abstract: To study the mechanism of sodium citrate interfering on corn starch gelatinization and film-forming ability, sodium citrates with levels of 0.0%, 0.05%, 0.1%, 0.2%, 0.4%, 0.8% were added in 5% starch suspension, that were mixed and heated to fully gelatinized.The swelling degree, solubility, transmittance, water absorption, retrogradation, electrical conductivity and IR photograph were examined.With same levels listed, sodium citrates were added in corn starch-glycerol-sodium alginate to form composite films. Mechanical properties, water vapor barrier property and transparency of the films were detected, and film's thermal stability was analyzed with DSC. Results showed that swelling degree, solubility, light transmittance, water absorption of corn starch raised as adding citrate sodium, while, starch 's retrogradation reduced; composited film's tensile strength, elongation at break, thermal stability were improved and the film's transparency and water vapor transmittance were reduced. Sodium citrate involved in starch gelatinizating and film-forming process in physical-chemical interaction of molecules, so as to effect the corn starch gelatinization and film forming ability.