Abstract: Starting from the three aspects of rain, water and hydrological monitoring and forecasting, an API model and synthetic flow method are used to carry out flood forecasting for the 2023 autumn flood in the Hanjiang River Basin in Xiangyang City, Hubei Province. The flood composition and flow superposition synthesis principle of the Hanjiang River Basin in Xiangyang City, the method of determining the current time of flood peak, and the method of calculating the flood peak water level of Xiangyang Station are summarized. In view of the problems found in the review analysis, such as large runoff prediction error, insufficient water conservancy project scheduling information, and disordered water level flow relationship, it is proposed to master the flood evolution law of the Hanjiang River Basin in Xiangyang City, divide the interval runoff prediction node in detail, scientifically apply rainfall runoff forecasting, optimize production confluence parameters in time, and build an upstream and downstream joint forecasting and scheduling system based on digital twin basin and digital twin water conservancy engineering systems, which is an important means to further do a good job in flood forecasting in the Hanjiang River Basin in Xiangyang City.