Abstract: In this paper,the comprehensive studies are carried out on the tectonic characters of the front margin along the middle section of the Longmenshan Overthrusting Belt based onthe analysis of dynamics,kinematics and geometric deformations on the overthrusting beltwith the example from the Yazi River Strticture in Peng County,west Sichuan.It is proposed that the tectonics of the front margin along the middle section of the LongmenshanOverthrusting Belt shotild be a superimposed duplex tectonic characterized by a buried overthrusting tectonic model,of which the major detachment is not outcropped.The transformation of the detachment into decoupling structure brought about the stress reliefzone of front delta-belt while the multiple superimposition and increasing thickness of theimbricated overthrusts should consist of a number of low angle overthrusts between theroof and footwall of the major detachment.