To know the velocity distributions in ship wake is one of the most essential problems in ship design. Here a method is proposed to estimate them and some results of numerical calculations are shown compared with those of experiments. The velocity is assumed to consist of the potential and the viscous components. The former is calculated from the source distributions which are obtained from the wave analysis and the hull surface condition. The latter is calculated as induced velocity of vorticity distributed in the two. regions, one is the boundary layer on ship surface and the other is the ship wake. For the boundary layer, the three dimensional turbulent boundary layer calculations are carried out and the vorticity distribution and the separation position are determined. On the other hand, the vorticity in ship wake is assumed that it is diffused from the boundary layer which can be estimated by solving the diffusion equation. The estimated vorticity and velocity distributions show fairly well agreements with those of measurements. As an application of this method, the viscous resistance is calculated from the estimated velocity distributions, which shows a little smaller resistance coefficients than those of the wake survey.