Abstract: Addressing the issues of inadequate river regulation and storage space, ineffective utilization of rain and flood resources, insufficient water supply capacity, constraints on water resource development and utilization, poor connectivity of water systems, and inadequate regional water environmental capacity in the Shuyang Yellow River old course area, this study embarks on research on water resource allocation based on rigid constraints. The aim is to promote the optimal allocation of regional water resources and enhance the water conservancy guarantee capability. Under the requirements of rigid constraints on water resources, three levels of water demand—rigid, semi-rigid, and elastic—are proposed from the water demand perspective. A genetic algorithm is employed to establish a rigid constraints water resource allocation model to allocate the available water volume for rigid water demand in the Yellow River old course area. The results show that the available water volume under the current engineering conditions in the planning level year cannot meet the rigid demand under the 90% guarantee rate in the planning level years 2025 and 2030. Therefore, it is necessary to increase the external adjustment of available water volume in the future, and three major projects such as the Longgang Hub Project, the Zhuhai Station, and the Yanghe Diversion Project could be constructed. This allocation scheme can provide scientific and technological support for water resource assurance for the construction of the Shuyang Yellow River Old Course Ecological Prosperity Corridor.