The water flow situation in the confluence area of straight braided reaches is complicated. If the entrance area of a ship lock is arranged in the mixing area of the confluence river，navigation problems such as flow pattern disorder occur，which is not conducive to the navigation safety of the ship lock. Therefore，the three-dimensional（3D）numerical flow simulation technology of the Mike 3FM module is used to obtain a sufficient understanding of the characteristics of the flow pattern at the entrance area of the ship lock at the bar tail. Specifically，we study the 3D flow pattern at the entrance area of the ship lock in the Taoyuan junction built in the lower reaches of the Yuanshui River and mainly obtain the distribution characteristics of the planar flow pattern of the discharge flow at the entrance area of the ship lock at the bar tail in the braided reach in the middle flood period，as well as the laws of the main flow zone，mixing zone，and dynamic axis of the confluence. The research can provide a theoretical basis for relevant research on the design of a new ship lock and the upgrading and reconstruction design of an old ship lock in braided reaches.