The crosslinked and relaxed molecular models of the EPON 862 and DETDA system were constructed using a computational molecular dynamics method under a reactive force field. The methodologies for evaluating and validating the models are described, and the effect of temperature on the elastic and yielding behavior of EPON/DETDA structures are presented. The elastic properties of epoxy materials, such as Young’s modulus and Poisson’s ratio, and also the yield strength, showed a remarkable response to temperature changes. The predicted data were validated with experimental data found in the literature.