With the rapid development of the marine economy, marine operations are gradually diversified. To improve the hydrodynamic performance of SWATH in offshore working conditions, a design optimization method for Small Water-plane Area Twin Hull (SWATH) considering the resistance and seakeeping performance is proposed. The automatic optimization design of SWATH hull form with minimum resistance at different speeds is carried out to obtain a set of Pareto optimal solutions. Then the seakeeping performance of the original and the Pareto optimal solution set are predicted. On this basis, a comprehensive evaluation method based on the composite weight factor of SWATH resistance and seakeeping performance is provided. The results show that the method can obtain a hull form scheme with better hydrodynamic performance than the original hull form. In addition, it can guide the hull form optimization design of SWATH.