Abstract: An extended GIM (group interaction modelling) method was developed by considering the influence of conversion on the cohesive energy and the degrees of freedom of epoxy resin system, which can predict the relation between conversion and material properties of epoxy resin. The epoxy resin composed of epoxy EPON862 and curing agent DETDA was used as an example for validation of the extended GIM method. It is found that the extended GIM method not only accurately predicts the material properties of fully cured EPON862/DETDA system, including glass transition temperature, volume shrinkage, coefficient of thermal expansion and elastic modulus, but also well captures the trend of these material properties changing with the conversion throughout curing process. And good agreement is found by comparing predicted results with that obtained from the molecular dynamics (MD) simulation and experiments. As combined with curing kinetics, this extended GIM method is capable of providing accurate material properties as the input parameters for modelling the shrinkage strain and residual stress throughout the curing process of epoxy resin.