MS 8.0 Wenchuan earthquake on May 12,2008 caused Beichuan county massive damage,and resulted in more than ten thousands deaths.The whole Beichuan county town has become ruin.Based on the field seismic investigation,three principal causes of building and road＇s serious damage as well as personnel heavy casualties are given：the ground surface rupture effect caused by seismo-active fault movement,the secondary geological hazards （collapse and landslide） and the vibration failure effect caused by strong ground motion.Damage of buildings along the main fault and secondary faults were more serious,but destruction in adjacent buildings is relatively not severe.The Wangjiayan landslide and Jingjiashan collapse brought about huge damage to the Beichuan county town and led to more than 2000 people death.The effects of vibration failure were ubiquitous for all buildings,especially horizontal shear movement generated serious constructional damage.