Epoxy resin in the core of the reactor bears combined effects of thermal, mechanical and other stresses during operation, which can cause changes of its physicochemical structure and mechanical properties, thereby affecting the safe and stable operation of the reactor. In this paper, epoxy resin samples are subjected to thermal oxygen aging and mechanical aging through accelerated aging tests, the microstructure and mechanical properties of samples are analyzed through SEM and MTS testing. The results indicate that thermal oxidative aging can generate new chromogenic groups, deepening its color. The effect of mechanical stress makes the epoxy resin matrix more compact, resulting in mottled cracks on the surface. Microscopic observations show that thermal oxygen aging has a significant promoting effect on the aging modification process of epoxy resin. The curing process or a single mechanical aging has a relatively small impact on epoxy. When thermal and mechanical stresses work together, the degree of looseness and porosity on the substrate surface are higher than when a single aging stress is applied. By analyzing the mechanical properties of epoxy resin in different aging states, it is found that prolonging the curing time significantly enhances the hardness of the epoxy system. During the process of thermal aging, mechanical strength of epoxy decreases first and then increases, with both damage and enhancement effects present. Mechanical aging has a compression effect on the epoxy matrix, which increases the elastic modulus of the epoxy in the early stage of operation.