In this paper, a numerical study on the behaviours of a ship passing through a lock under the influence of a berthed ship is carried out. The viscous flow and hydrodynamic forces are calculated by applying an unsteady RANS code with a RNG k-å turbulence model. UDF is compiled to define the ship motion. The numerical results are obtained and analyzed for the cases of the berthed ship at different longitudinal and transverse position in the approaching channel to investigate the influences of the berthed ship’s postion on the ship-ship and ship-lock hydrodynamic interaction.