Abstract: The interfacial reinforcement mechanism of composite sandwich beams has been studied by experiment and numerical method. The sandwich beam specimens were manufactured by the vacuum assisted resin injection process and an experimental investigation was also performed to determine interfacial fracture toughness for the sandwich specimens with and without chopped fiber reinforcement. A meso-mechanical model considering energy dissipation was adopted to describe the process of single fiber peeling and pull-out as the crack extended. And a stochastic uniform distribution model was established to characterize the energy dissipation of overall chopped fibers per unit area. A finite element model was used to simulate the process of interfacial crack growth for a double cantilever beam. A nonlinear spring element was employed to account for bridging stress caused by the chopped fiber and the energy release rate was calculated by the virtual crack closure technique. Some numerical results and discussions were given for verifying the validity of the meso-mechanical model with stochastic distribution provided. The experimental and numerical investigation indicates that the chopped fiber reinforcement was an effective technique to improve the load capacity and interfacial toughness of the sandwich structures.