Honggu Tunnel is the first immersed tunnel in river with large flow velocity and large water level drop.The tunnel segment floating transportation is difficult. The risk nodes in segment floating transportation of the tunnel are analyzed so as to guarantee the safety of the segment and surrounding buildings. The water resistances on segment at every risk node are numerically simulated; the calculation software Fluent is adopted; and the calculation model is based on RNG κ-ε model.Some suggestions are proposed as follows: 1) The segment undocking should be carried out under the flow velocity of less than 0.6 m/s. 2) The segment turning should be carried out under the flow velocity of less than 08 m/s. 3) The segment passing through Nanchang Bridge should be carried out under the flow velocity of less than 1.0 m/s. 4) The optimized segment turning scheme of river course widening can meet the requirements of segment turning and anchoring.