The properties of four kinds of flexible epoxy resins C22 DGE,C22 TGE,C21 DGE, C36, DGE were compared with each other. By TG-DSC, the active energy and enthalpy of curing reaction of flexible epoxy resin were further researched. The relationship between heat-resistance and mechanical properties of cured products of flexible epoxy resins and their structures were studied. It was found that the curing reaction of flexible epoxy resins with anhydride was particularly complex and heat-generating, the enthalpy of C22 TGE/THPA, C22 DGE/THPA, C21 DGE/THPA, C36 DGE/THPA were 173.35,131.83,155.67,102.46 J/g and the active energy of curing systems were 79.4, 56.99,91.30,70.90 kJ/mol, respectively. The curing products of longchain epoxy resins with anhydride bad a superior impact-resistance and flexibility to bisphenol A epoxy resins,but junior heatresistance to bisphenol A epoxy resins. The flexible epoxy resins could be applied in the flexible conditions, but not including on the condition of high temperature.