For the complicated navigable condition of Mujing ship lock expansion project,we carry out an experimental study on the navigable flow condition in the upstream and downstream approach channels of recommended schemes. On the basis of the hydraulic model test,we use the small-scale ship model measurement and control technology to observe and analyze the navigation parameters,such as rudder angle and speed.The results show that when Q≥3 900 m3/s,there are some parameters exceeding the limit both in the upstream and downstream approach channels,which may lead to a dangerous navigation;for both upper and lower waterways,the entering of the lock is more difficult than getting out of it and the navigation difficulties are on the turning section and the guard-wall end respectively,where the velocities of cross flow are relatively high.From the comprehensive analysis of the study results,a maximum navigable discharge of 3 000 m3/s is proposed,which provides a scientific and reliable data basis for the optimal design and later operation of the ship lock project.