Abstract: As one of the main thin-walled energy absorption structure in automobile, the top-hat beam draws great attention and its performance improvement is a concerning issue. Research indicates that the energy absorption performance of thin-walled structures can be improved by the wall thickness optimization. However, complicated thickness distribution would cause manufacturing difficulties. Thus, it is urgent to develop a design optimization method of structural thickness distribution based on specific manufactory process technology. In this paper, a design optimization method is proposed for maximizing the energy absorption of top-hat beam under transverse crash manufactured by variable gauge rolling technology. This top-hat beam is made of tailor rolled blanks, and can be classified as uniform thickness sections and transition sections. Through adjusting the length and thickness of the uniform section, and the description of the transition section, the performance of the structure can be optimized. To find the optimal structure parameter, we use the hybrid cellular automata to determine the optimization direction. To meet the variable gauge rolling constraint, the structure is filtered in the iteration. Based on this method, we studied an example of top-hat beam and found its optimized section length, thickness and transition description, which shows the effectiveness of this method.