The comparative research on Particle Swarm Optimization (PSO) and the Serial -Niche Particle Swarm Optimization (SNPSO) to gain a optimal side-hulls's arrangement of trimaran. With stretched technology in object function, SNPSO improve the velocity of constringency and the efficiency of exploiture. Using the SNPSO in the arrangement of side-hulls, overcoming the disadvantage of losing the optimal arrangement in experiment research. The convergence results of PSO and SNPSO in the arrangement of side-hulls are accordant, but the SNPSO performs well than PSO in convergence and exploitation in numerical experimentation.