The low waterway grade of Mengli hydro-junction is not able to meet the requirement of the current freight growth.So,it is necessary to build the second-line shiplock on the right bank of the first-line shiplock to increase the shipping capacity.The overall fixed-bed model is established to study the effect of the guide wall length and the layout form on the flow conditions in the entrance area and the approach channel.According to the model test results,the navigation flow conditions of the modified scheme II，with the separately arranged first and second-line shiplocks,the guide wall length of 375 m and the holes in the wall head,are best among all the modified schemes:the navigation conditions of second-line shiplock are improved while the ones of the first-line shiplock almost keep unchanged,and the unfavorable flow conditions in the entrance area and connecting section are improved.