Abstract: The flow condition of the approach channel and its entrance in ship locks which are arranged parallelly is a key problem to scholars. An unreasonable layout of locks may lead to safety problems during operation. A physical model test with the scale of 1:100 is carried out to study the flow conditions of different layouts of the second line ship lock at the Guigang navigation junction. Based on the characteristics of the Guigang junction, the flow conditions of the approach channel of the second line ship lock, and the mooring section and the entrance of the first line are analysed under different discharge conditions. Then the control working condition affecting the flow of the approach channel is obtained, based on which the optimized layout schemes are proposed. The flow conditions of the approach channel in different optimized layouts are compared. According to the results, the scheme with the length of guide wall being 135 m and the height of cross section at the bottom of guide wall being less than 0.5 m is recommended. This study can provide a reference for the optimal design of the Guigang second line shiplock.