Abstract: The Mengwa Flood Detention Project is an important component of the flood control system in the middle reaches of the Huai River, and is also one of the most frequently utilized flood detention areas in China. Its construction and operation have led to significant transformations in flood control pattern and agricultural productivity. A comprehensive overview of the Mengwa Flood Detention Project, operational conditions, and its 72-year operation history is presented. Literature records and empirical data are employed to evaluate the agricultural benefits of theMengwa Flood Detention Area during the period from 1952 to 2023 based on counterfactual method. Results indicate that a substantial reduction in the occurrence of flooding with the construction of the Mengwa Flood Detention Project. Over the 72-year period, the total harvest counts in agriculture increased from 72 times to 129 times. The cumulative harvested area expanded by 1074500 hm², resulting in an additional 6 billion kilograms of grain production. The cumulative land use benefits escalated from 8.2 billion yuan to 22 billion yuan.Finally, the inspiration from the construction and operation of the Mengwa Flood Detention Project is summarized, in order to provide important reference value for the construction and management of flood detention areas in the Huai River and other river basins.