Gaoliangjian lock is composed of the expansion shiplock and the second-line shiplock, which is a type. The double lock shares the lower approach channel and confluences with the North Jiangsu Irrigation Canal at a short distance. The flow conditions in the under approach channel are quite complicated due to the emptying courses of the double lock and the North Jiangsu Irrigation Canal. The flow characteristics under different combinations of typical water levels and operation modes are studied by numerical simulation. Considering the lock features, the currently most convenient and effective structural measure, separation levee, is proposed. The results can be used for the lock design and management.