For the problem of navigable flow condition of an expansion project of a ship lock in narrow reach in mountainous area,we apply a physical model with a scale of 1100 for the Mashi lock in Rongjiang River to investigate flow conditions of the low approach channel.The results show that using a guiding wall with bottom ports and optimizing the radius of curvature can improve the corresponding flow conditions significantly.We recommend that the length and radius of curvature of a guiding wall are 126 m and 500 m respectively,six ports and the width and minimum height of every port are13 m and 4 m respectively.The achievement can provide references for the similar projects.