Abstract: The Xianshui River fault zone,located in the central part of the Songpan-Garze orogenic belt,divides the belt into two parts,The revelation of extensive ductile shear strain is based on the discovery of granite mylonite along the fault zone In this paper,the authors discuss the mechanism,temperature and the phases of deformation,and then analyze the kinematic and dynamic characteristics of the Xianshui River fault zone,and its effect on the Songpan-Garze orogenic belt The Xianshui River fault zone,still active today,is a large scale high temperature left-lateral ductile shear zone which has undergone polyphase activity and transformation from ductile to brittle strain since the Miocene The displacement along the fault is over 80-100 km The large Zheduoshan granite is the syn-tectonic Product of left lateral ,ductile strike slip of the fault zone.