The How mechanism near the groin-like structure and two-dimensional model are presented in this paper. The velocity distribution behind the groin-like structure is found to be self-preserving in character. Hence, the Reynolds cquations can be transformed into an ordinary differental equation by similarity and the equation of velocity distribution behind the groin-like structure is obtained. The calculated results are in a good agreement with the experimented one. In addition, the turbulent viscosity along the main flow direction is briefly discussed. The How mechanism near the groin-like structure and two-dimensional model are presented in this paper. Therefore, the Reynolds cquations can transformed into an ordinary differental equation by similarity and the equation of velocity distribution behind the groin-like structure is obtained. The calculated results are in a good agreement with the experimented one. In addition, the turbulent viscosity along the main flow direction is briefly discussed.