Abstract: The sponge green open space from the perspective of landscape architecture plays an increasingly important role in the regulation of urban rainwater. The sponge green open space in semi-humid areas has remarkable characteristics. Summing up the design method, we can provide reference for the related research and practice of landscape architecture industry. This paper takes the whole process of green open space construction in Binhu East Road of Qian’an City, Hebei Province as the research object, ensuring the basic functions of green open space and reducing the external runoff in the green open space as the premise, and the rainfall characteristics of the semi-humid areas as the research basis, to put forward the design method for exogenous runoff type sponge green open space in the semi-humid areas. For the Low Impact Development (LID) system inside the green open space, the XPdrainage software is used to simulate the runoff discharge process under different recurrence period rainfall conditions before and after the site development, and the total runoff, peak flow and peak occurrence time of the two is compared and analyzed. Conclusion: 1) Under the different recurrence period rainfall, the green open space is significant in the regulation and storage of runoff in Binhu East Road; 2) The exogenous runoff type sponge green open space in the semi-humid areas needs to be designed in a scientific quantitative way combined with landscape treatment.