In view of the cost benefit evaluation of the current sponge city construction, the second construction phase of a new hospital in a city in Jiangsu Province is taken as an example to carry out the research. Different sponge city facility combinations are chosen in accordance with the various situations of the construction site. Storm water management model (SWMM) is adopted to conduct simulations of the stormwater management effects of different sponge city facility combinations under various rainfall conditions at the site, and then the cost benefit evaluation is conducted based on life cycle cost. The results show that sponge facilities can effectively strengthen urban stormwater management, reduce peak runoff by 53.32%-70.14% and outlet flow by 6.67%-53.33%. The stormwater management capacity and cost benefit value of different sponge city facilities are negatively correlated with the intensity of the rainstorm. Among them, the runoff control amount and cost effectiveness per unit area of the sponge facilities with permeable subsurface are higher than those with impermeable subsurface. The research results are of referential value for the design of sponge cities on the site scale.