A numerical analysis method of the thermal stability of the resin concrete is proposed in this paper. A 3D aggregate accumulation model based on the predecessors theory is established and a 2D cross section is directly captured from it. In order to simplify the analysis, a kind of conversion program is developed. The thermal expansion coefficient of established model is close to previous research results. It confirms the analysis method is correct. By the results, a reliable formula is found to calculate the thermal expansion coefficient and a method to reduce the thermal expansion coefficient of resin concrete is proposed.