Abstract: The paper has further discussed the dynamic mode of Longmen Mountain-West Sichuan Foreland Basin System, which is Longmenshan subduction (simply called L-type Subduction).It is further confirmed through the physical simulation and mathematic simulation that L-type subduction existed in the a-rea.The gravity and adjustment of deep material had taken an important role in the process of the formation and evolution of Longmen Mountain-West Sichuan Foreland Basin System.The dynamic source, formatting L-type Subduction, was from the deep.The deep dynamic force took the role depending on the main deep faults.There is a tendency that the relative displacement of the main faults decreased from the deep to the shallow.The plastic and soft layers and the sliding on them had taken an important role in the formation and evolution of Longmen Mountain-West Sichuan Foreland Basin System.The horizontal relative displacement of Mantle plastic layer is usually greater than the horizontal relative displacement of Crust plastic layers.