The designed highest navigable water level is one of the key technical parameters of ship lock construction,which directly affects the capacity,construction period and investment of the ship lock.For the value of the highest navigable water level of Zhuzhou second-line lock project design,we analyze the designed water level of the junction and the flood time in different recurrence periods according to the hydrological characteristics of the flood surge and collapse and the short peak time at Zhuzhou junction,and expound the navigable flow condition at the lock’s entrance area,waterway navigation condition and the investment of the second-line lock project under different characteristic water levels. Adopting the method of model test verification and investment calculation and comparison,we come to the conclusion that the highest navigation water level of Zhuzhou second-line lock design should adopt the flood standard once every 10 years.The research method can be used as reference for the lock expansion project in the mountainous and hilly areas.