We propose a multiscale simulation strategy to study the interplay between diffusion and curing reaction on the network formation and the corresponding mechanical properties of epoxy resins. Atomistic molecular dynamics simulations are first used to estimate the parameters that will be used in coarse-grained simulations. Then a dissipative particle dynamics coupled with curing reaction model is developed and adopted to simulate the cross-linking process of the system to form an epoxy network structure. We find that, during the curing process, to which extent that the components can diffuse between each other greatly influences the generated network structure. Finally, the reverse mapping of the coarse-grained structure to atomistic representation is carried out to analyze the mechanical properties and the Tg of the epoxy resin system.