<p>Active tectonic movements and geological disasters frequently occur in the upper reaches of the Jinsha River, increasing the likelihood of landslides obstructing the river. Taking the ancient Rongcharong landslide dam failure events in the Suwalong reach as an example, this paper first analyzes the accuracy and applicability of the commonly used methods in calculating the peak flow of the dam failure, such as the empirical formula, the numerical method based on the physical mechanism, and the computational fluid dynamics (CFD) method. Then, the peak flood flow of the Rongcharong-dammed lake when it overflows the dam is determined to be 28 393–64 272 m³/s. At the same time, the failure process of landslide dam due to flood erosion was elucidated using the CFD method, which can be divided into three stages: gradual erosion in the initial stage, rapid development in the middle stage, and gradual expansion in the final stage. Finally, the factors that affect the peak flow of floods are analyzed, and suggestions for emergency treatment of landslide dams are put forward. The findings of this research can serve as a valuable reference for disaster prevention and mitigation strategies to adapt to the increasing frequency of landslide-induced river blockages.</p>