Abstract: In the process of designing rainwater harvesting green space, the present method of determining the scale of low impact development (LID) facilities is based on single objective, which is lack of evidence and inefficient, hence the connection between rain flood simulation and design process is poor. This study attempts to establish a multi-objective optimization platform in the parameterized design platform Grasshopper, setting the effect of stormwater control and construction cost as the objective functions, and using NSGA-II algorithm to determine the scale of LID facilities. The results serve as a quantitative basis for the scale design of LID facilities in the early stage of design. In addition, the new platform is applied to the rainwater harvesting green space design project of Nanyang Academician Town, and compared with traditional development methods. The results show that in the study area, properly increasing the proportion of permeable pavement and bio-retention cell is conducive to improving the performance price ratio of LID facilities. The more cost input of LID facilities would not lead to a better result, so it is necessary to select an appropriate one according to the requirements of sponge-city documents. The research results can provide new ideas for the design of rainwater harvesting green space in the future.