The lowest navigable water level in the upstream design is one of the key technical parameters for ship lock construction,which directly affects the performance,investment and duration of the lock.In the light of the value of the lowest navigable water level in the upper reaches of the built ship expansion project,we analyze the actual minimum operating water level and the guaranteed level water level according to the measured water level of the Zhuzhou junction,and discuss the investment situation of the second-line lock project,the operation situation of the first-line lock and the connection of the water level between the channelized cascades under different characteristic water levels.The conclusion is drawn that the lowest navigable water level of the upper design of Zhuzhou second-line lock should be 38.3 m by means of model test verification and investment comparison.The research method can be used as reference for the lock expansion project in the mountainous and hilly areas.