One of the reasons making the optimal design for a stern shape of a ship hull still difficult even nowadays is the complexity of flow field behind a transom stern. Study on effects of transom configurations on flow fields as well as on the ship resistances is therefore necessary and useful for the transom shape optimization. In this paper, the simulated results of flow fields behind transom stern of a container ship hull with various transom configurations using a CFD method are presented. Transom stern of an original container ship hull is modified in both breadth and height to get new models with various stern shapes. A flow solver which solves the Reynolds Averaged Navier-Stokes (RANS) equations for incompressible flows is employed in the computations of flow fields around ship hulls. The computational results are compared with each other to investigate correlations of the transom shapes with flow fields behind the ship stern and ship resistances. It is considered that the achieved results provide useful information for the practical optimization design of a stern shape of a ship hull.