Abstract: A series of epoxy coatings with different contents (0-15.15%) of epoxidized soybean oil (ESO) were prepared by adding ESO into the system of bisphenol A epoxy resin (DGEBA) and modified diethylenetriamine (DETA). Critical stress-intensity rupture strength factor (KIC) of the modified coating was tested according to three-point bending test and curves of mass gain and time were obtained by static immersing test, and the glass transition temperature Tg was tested. The diffusion coefficient D of water molecules in modified coating was calculated. The results show that KIC increased and then decreased, Tg and mass gain decreased gradually, and D decreased and then increased with the increase of ESO content. When mass fraction of ESO was 7.35wt%, the anti-water molecules diffusion coefficient of the modified coatings was the best.