The second-line ship lock is planned on the right of the first-line ship lock，but the flow pattern in the approach channel is very complex when the double locks are irrigating or draining.Adopting the volume control method，we establish a two-dimensional mathematical numerical model of hydrodynamics to evaluate the navigation condition of the approach channel.The calculation results of various working conditions show that double locks’ simultaneous running is the most disadvantageous.In this case，the minimum water depth of the lower approach is enough，however，the flow rate is too large，and there is a certain impact on the safety of the ship.According to the calculation results，the relative displacement of the discharge time can reduce the maximum longitudinal velocity.