In order to lessen the pressure of flood prevention of middle and down stream in Yangtze River, water level of Qingjiang Geheyan was more than 3 meters higher than normal water level in some times in August, 1998. The method to establish deformation forecast models of dam is introduced in detail by taking deformation observation datum of some monitor points of Qingjiang Geheyan dam.Finally, the effectiveness of this method is verified by a practical example.