The daily failure of the ship lock reversed tainter valve is the damage of the top water seal. Especially when the reversed tainter valve is opened, the top water seal and the gate lintel are separated to form a narrow gap. The stress on the water seal is terrible, causing the water seal to be easily damaged. The modification of the top water seal device from improving the fixation reliability of the water seal and the force are studied. The issues in the existing fixation methods of the water seal are analyzed. Perforated bolts and two nuts are used to fix and prevent loosening to improve reliability. Water retaining plates are added to the water seal on the test device, then the force state of the water seal is tested. The results show that the cavitation of the water seal is weakened. The hydrodynamic time-averaged pressure load is reduced. The self-excited vibration of the top water seal can be suppressed, and the force state of the water seal is improved. In the overhaul of Gezhouba No. 3 ship lock in 2022, the top water seal device of the reversed tainter valve is modified, and the operation effect is good after the modification.