When a ship is moving in lateral direction at berthing in a harbour or when a ship is moving with large drift angle at low speed, it is known that the component of cross flow drag dominates the hydrodynamic force acting on ship hull. It is important to develop prediction method for the cross flow drag from the view points of safe navigation of ships at low velocity in harbour or restricted water. The authors has proposed the prediction method for the cross flow drag acting on a ship hull based on the vortex shedding model in previous paper. However, the prediction method requires to determine parameters α which reduces strength of the free vortices shed from the ship hull. In this paper, we improved the vortex shedding model considering damping of the free vortices. It is shown that longitudinal distribution of the cross flow drag along the ship length can be predicted with comparatively high accuracy using the presented prediction method.