The purpose of this paper is to introduce the topology optimization method into the lattice style design for the rapid casting SL patterns. During the burnout procedure of the SL resin pattern, the thermal expansion will lead to the crack of the ceramic shell and fail the investment casting. Therefore, the SL patterns are always designed hollowed and some lattice styles are used to fill the cavity to solve the problem. In this paper, we propose to carry out the structural design by assigning the inner part of the SL pattern as the design domain where the material distribution is optimized with topology optimization. The idea is 1) to save the cost of the resin material, 2) to solve the crack problem of the ceramic shell and 3) to maintain certain stiffness for the pattern itself. As a result, we choose to minimize the thermal stress in the ceramic shell as the design objective with the stiffness and material cost of the SL pattern constrained to certain values. The topology optimization is implemented with different definitions of design domain in this paper. Various optimal results are obtained numerically. By comparing the optimal design with the existing lattice style, the newly obtained designs have shown better performances in reducing the stress in ceramic shell and maintaining the stiffness of the SL pattern.