Epoxy resins are critical materials in aerospace applications, yet their mechanical properties, specifically the tensile modulus, can be significantly compromised when exposed to electron irradiation in space environments. To thoroughly examine this degradation, we developed an integrated research approach combining vacuum electron irradiation experiments with multi-scale simulations. Coarse-grained (CG) and Monte Carlo (MC) methods were employed to generate the necessary models and primary knock-on atom (PKA) data, while molecular dynamics (MD) simulations were conducted to model the irradiation and tensile processes. Our findings reveal that the tensile modulus percentage loss of epoxy resin stabilizes as the irradiation dose approaches 1.0×101⁵ eV/cm2. The strong agreement between experimental and simulation results validates the accuracy of this methodology. In the epoxy resin systems studied with different degrees of cross-linking, irradiation leads to an increase in the tensile modulus of the low cross-linked structures with a maximum increase of 21.46%, and it leads to a decrease in the tensile modulus of the high cross-linked structures with a maximum decrease of 8.03%. This multi-scale approach has been successfully applied to investigate the trends and causes of tensile modulus changes in epoxy resins after electron irradiation. It can be used to explore the changes in the properties of a wider range of polymers after irradiation.