In order to accurately reconstruct the process characteristics of “23·7” catastrophic flood and provide theoretical support for the prevention and early warning of catastrophic floods in the Yongding River Basin, the grid-based Xin’anjiang (Grid-XAJ) model and Grid-XAJ based on saturation-infiltration double excess (Grid-XAJ-SIDE) model were used to simulate and analyze five key control sections in the Yongding River Basin: Zhaitang Reservoir, Qingbaikou, Yanchi, Sanjiadian, and Lugou Bridge. Typical flood events from 2000 to 2022 were selected for parameter calibration, and the “23·7” catastrophic flood event was used for validation. The results show that both the Grid-XAJ and Grid-XAJ-SIDE models can accurately simulate the entire process of the “23·7” catastrophic flood. In the Qingbaikou section, the determination coefficients of both models achieve Class A accuracy; at the Yanchi, Sanjiadian, and Lugou Bridge control sections, the model accuracy reaches Class B, indicating excellent simulation performance. The study demonstrates that the Grid-XAJ and Grid-XAJ-SIDE models perform well in simulating flood volume, peak flow, and peak time at the five control sections, making them effective for simulating catastrophic floods in semi-arid and semi-humid regions.