The second phase cofferdam of Yakou navigation hub adopts a new composite structure featuring river sand filling，slope protection with tube of sand filling，composite geomembrane anti-seepage，geotextile anti-filtration，and polypropylene fabric anti-scouring，and the overtopped condition is easy to induce the instability of cofferdam.Based on the experimental data，this paper analyzes the stability and safety of cofferdam under complex working conditions from the perspectives of seepage，stress and deformation，and stability and compares the stability of geotextile，polypropylene fabric，and tube of sand filling layer.The results show that the effect of an overtopped cofferdam on the slope foot seepage gradient is obvious，and the local resistance to seepage damage can be enhanced after reinforcement.The overtopped condition is the most unfavorable to the stability of the side slope of the foundation pit of the cofferdam，but the overall stability and stress and deformation meet the requirements of the code after reinforcement.The friction between polypropylene fabric and tube of sand filling is small，and there is the possibility of interlayer displacement，but the geotextile between polypropylene fabric and tube of sand filling can effectively improve the stability between layers.After the test of the severe Hanjiang River flood in the autumn of 2021，the cofferdam can run stably and safely under water retaining and overtopped conditions.