So far there is no standard at home and abroad that can be referred to in the design and construction of large crosssection waterway tunnels. In the paper, the design of the crosssection of Fuchunjing waterway tunnel is studied. The requirements for the crosssection of the underwater part of the waterway tunnel, the construction clearance of the abovewater part of the waterway tunnel and the navigation safety guarantee measures are analyzed. Optimization design is made on the inner contour of the waterway tunnel by means of optimization method and analysis, considering the mechanical characteristics of the surrounding rock and the tunnel structure. The crosssection of largesized waterway tunnel that can meet the requirements of Grave IV single shipping lane is proposed. It is suggested that the crosssection with curvedwalls should be adopted, considering the economic efficiency and structure force.