Abstract: A ship, especially a larger one, has to take an appropriate start position in a river to smoothly travel through a river bend. That start position has been chosen according to experience gained in long navigation practice. A pithy formular "taking higher side and aiming for lower side" has been the general guidance. This paper quantitatively analyzes the process of ship travelling through a river bend and develops a method to calculate the position where a ship starts to sail through a river bend according to actual water flow in the river. A positioning model is built based on ship motion process and the ship lateral displacement and track width are calculated against the yaw angle and transverse flow by means of Matlab. The position the ship should take before starting to travel through a river bend is decided based on the calculation results. The calculation for Yingongzhou curved waterway is checked through simulation and proved.