Stereolithography (SL) based investment casting, also known as the rapid casting, is a new casting technology which uses the SL rapid prototyping model as the expendable pattern.However, many problems have to be solved to improve the efficiency and reliability of the rapid casting procedure.One of the key difficulties is to avoid the crack of the ceramic shell during the burnout of the SL pattem.Normally the SL epoxy resin is a thermoset material whose coefficient of thermal expansion (CTE) is 10 times higher than the CTE of the ceramic shell.During the heating procedure, a significant thermal expansion of the resin pattern will unfortunately break the ceramic shell and fail the investment casting.Actually, to solve the problem, it is found that the resin pattems have to be produced much weaker to lower the thermal expansion force loaded on the ceramic shell.The practical SL patterns are always designed as hollowed and some heuristically designed periodic lattice structures are used to fill the cavity.The purpose of this paper is to demonstrate the necessity of topology optimization design for the SL based investment casting resin model.In this paper, we first present some numerical analysis of the SL resin patterns filled with existing lattice structures.Both the thermal expansion and the mechanical loads are taken into account and applied on the resin pattern.By evaluating the stress level in the ceramic shell and the stiffness of the resin pattern itself, it is found that the existing solutions do not perfectly adapt to arbitrary patterns with different geometry design.Later, the lattice structures are further designed with topology optimization for different SL patterns.The inner part of the resin pattern is assigned as the design domain.The topology optimization is to find a proper distribution of the resin material to reduce the stress level and maintain certain stiffness for the pattern.By comparing the optimal design with the existing solutions, the effect of topology optimization is significant.The newly obtained designs have shown better performances.