For further increasing the passage capacity of the Three Gorges ship lock，we propose the synchronous navigation technology of large aspect ratio ships with 4.5 m draught. We discuss the feasibility of this technology from two aspects including ship berthing safety and navigation safety through systematic actual ship test. The results show that the mooring force of the ship exceeds 200 kN in three typical periods of braking stop，filling and discharging the lock chamber and opening the miter gate. The mooring force is closely related to the ship displacement，the inertia water level difference and the initial water depth of the lock chamber，and there is no obvious influence on the mooring force of the mooring type. Based on the ship sinkage formula built by the measured data，it is predicted that there is no bottom contact risk when the speed of synchronous navigation ships with 4.5 m draught is less than 1 m/s. The berthing safety of large-scale ships is the key problem that restricts the further increase of the capacity of Three Gorges ship lock，while the safety of navigation is not the control factor.