Under the background of global climate change, extreme hydrological events with increasing frequency pose severe threat to dam safety. Large floods in the Yangtze River Basin, accompanied by levee breaches, occurred in 2016 and 2020. On July 5, 2024, the embankment of Tuanzhou township in Dongting Lake area, Hunan Province, collapsed, endangering the safety of people’s lives and property. To expedite the return of residents to their homes and prevent secondary disasters, early emergency closure measures are typically implemented post-breach. At this stage, with equalized water levels inside and outside the polder, rapid emergency drainage is conducted under breach closure conditions. The impact of sudden water level drops on the safety of the main embankment and the secondary embankment has attracted significant attention, even constraining emergency rescue operations. To assess the effects of emergency drainage on embankment safety in the Tuanzhou polder of Dongting Lake area and aid in the formulation of emergency response plans, we constructed non-steady seepage and stability analysis model for the main embankment and the Qianlianghu-Tuanzhou interval embankment near the breach with Dongting Lake water level remaining unchanged. The analysis focuses on the seepage stability and slope safety of the embankment under extreme sudden water level drop rates of 0.3 m/d and 0.6 m/d during emergency drainage during breach closure. The results indicate that the maximum seepage gradient and slope stability of the embankment meet the standards for third-level embankment safety under various conditions. Additionally, we propose rapid drainage measures in comprehensive consideration of multiple factors to provide technical support for emergency rescue and shed new insights for safety analysis under similar conditions.