Abstract: In order to discuss the mechanical mechanism of composite soil nailing wall supporting foundation pit in practical projects, it was based on discrete element method of PFC^2D, and the introduction of particle flow theory and development of particle flow in mesoscopic numerical simulation technology, to conduct the mechanics studies about its mechanism from mesoscopic aspect for composite soil nailing supporting.The particle flow code model for composite soil nailing supporting was established by discrete element method, which compared with nailing supporting only and cement-soil pile supporting only, there were much difference about axial force and its distribution between composite soil nailing supporting and nailing supporting only.Whats more, the distribution of bending moment and shear stress is different from cement-soil pile supporting only.So, the results show it offers a new approach and method for mechanism study of composite soil nailing wall supporting foundation pit by using discrete element method.