There will be complex reciprocating flow in the middle channel of the dispersed cascade ship lock during the filling and discharging operation. In addition to the influence of the operation mode of the ship lock，the length，width，initial water depth and roughness of the channel will also have an important impact on navigable flow conditions. Taking the layout plan of the middle channel of the two-level double line lock as an example，the hydrodynamic characteristics，especially the influence law of the key parameters，are simulated by establishing a series of mathematical models. The results show that：1）The fluctuation characteristics in the middle channel vary greatly in different lock operation modes. 2）The increase of the width and initial water depth of the middle channel can significantly improve the flow fluctuation characteristics and can be used to improve the navigation flow conditions of the middle channel. 3）The increase of the channel length cannot effectively improve the flow conditions. 4）The roughness has no obvious effect on the improvement of various hydraulic indexes in the channel，but with the increase of the channel roughness，the overall water surface gradient in the channel decreases.