Abstract: Crown settlement is set to be the objective Tunnel function and efforts are put on searching tunnel shape which causes the least crown settlement.In this way,the safety of subsea tunnel can be guaranteed by controlling the formation and development of the cracks.According to the total-closure waterproof feature equivalent poisson ratio is adopted to apply ground pressure as well as water pressure which is a reasonable ways to simulate use FEM.Whole process optimization is put forward which contains optimization parameters acquisition,design variable sensitivity analysis and evaluation of the optimal design.According to the characteristics of subsea tunnel in Kiaochow Bay,optimization method mentioned above is used to make optimization analysis: crown settlement is reduced significantly after optimization;the optimum design set is made for the reference point to study the relation between crown settlement and design variables which can offer guidance for design;the stress state is also proved improved after optimization.