During the expansion of a second-line ship lock，constraints such as the terrain，construction，navigation，land acquisition and demolition，and investment should be comprehensively considered. Taking the Xiangqi second-line ship lock project as an example，this paper focuses on the design principles，site selection，and layout ideas and methods of the second-line ship lock and comparatively selects a layout scheme：It should be on the left bank of the first-line ship lock，and the distance between the axes of the two locks is 80 m，with the ship going straight in and curving out. We use the physical model test to analyze and optimize the navigable flow conditions of the entrance area and put forward the measures to improve the navigable flow conditions，such as extending the upstream and downstream partition walls，dredging the downstream riverbed of the power station，and optimizing the dispatching mode. Moreover，we propose the innovation and optimal design concept with strong universality for the floating access gates，breasting dolphins，and partition walls.