Abstract: Using the trapped waves data on different sections of Wenchuan earthquake region,the segmentation characteristic of the fault is obtained.Guanzhuang observation line is located at the northeastern portion of the fault,and the result indicates that the width of the rupture zone underground is about 160~180m.The center position of rupture zone underground corresponds to the surface breaking trace,and is equally distributed at the edges of the two fault walls.It reveals that,for the northeastern portion,the dip angle of the fault is greater and the fault is near vertical.However,Hongkou observation line is located at the southwestern portion of the fault,and the result indicates that the width of the rupture zone underground is about 180~200m.The rupture zone underground is mainly distributed below fault scarp.It reveals that,for the southwestern portion,the dip angle of the fault is smaller.The results will provide evidence for the research on the structure background of Wenchuan M_S8.0 earthquakes