Abstract: This study analyzes the ultimate strength of an ultra-large container ship in accordance with the requirements of the International Association of Classification Societies(IACS) to assess the reliability of its hull structural ultimate strength.. A twin-island ultra-large container vessel is selected as the research object. Based on IACS UR S11A the ultimate strength of the ship is calculated,validated,and subjected to reliability analysis. Results indicate that ship may face a risk of insufficient strength under extreme operating conditions,and structural reinforcement is therefore required in accordance with UR S11A. By innovatively integrating the requirements of UR S11A with structural reliability theory,this study realizes a quantitative assessment of the ultimate strength for ultra-large container ships. The findings provide reference value for inspection and maintenance recommendations for aging vessels,as well as for route optimization.