To analyze the influence of the environmental remediation project on the discharge capacity of the Pukou section of the Yangtze River, a twodimensional hydrodynamic model of the engineering section was established based on MIKE21 FM. The Moghadam roughness formula for submerged vegetation in the open channel was used to simulate the water resistance of vegetation and the influence of vegetation on the floodplains roughness and flood resistance was studied. Water level and velocity were selected as the observation indexes to analyze the changes of water surface line and the velocity distributions of floodplains and main channel with and without the vegetation on floodplains. The influence of vegetation on the flood discharge capacity under different discharge conditions was studied. The results show that the vegetation causes the upstream water level to rise, the water velocity of floodplains to decrease and the water velocity of main channel to increase. When the water depth of floodplains is less than the critical water depth (1.3m), the upstream banked up water level increases with the increase of the discharge. When the water depth of floodplains is greater than the critical water depth, the upstream banked up water level decreases with the increase of the discharge.