It is important to estimate the ship manoeuvring motion at slow speed. However, the manoeuvring characteristics of ship and the hydrodynamic forces acting on ship at slow speed complicate so much, because sway velocity becomes often larger than the forward speed due to the external disturbances such as wind and current. The development of prediction method for ship manoeuvrability at slow speed condition will be expected. In this paper, as the first step, the cross flow past rectangular cylinder in early stage from the rest condition are studied by vortex shedding model combined panel method, to analyze the characteristics of flow around ship moving transversely, taking into account the Kutta condition. Furthermore, the flows around some types of rectangular cylinders are calculated to check the validity of this method. From these studies, the cross flow past rectangular cylinder in the early stage from the rest condition will be affected by aspect ratio of cross section of the cylinder.