A new theory to estimate the state variables of flowing particles in a bin-hopper system was presented. The flowing behaviour of particles in the system was simulated by the particle element method. It was suggested that convergence of the flow path of particles in a hopper leads to a change in the bulk density of flowing particles, whereby particles in a hopper flow intermittently. On the basis of the microscopic behaviour of flowing particles observed through the simulation, a flow model was derived to analyse the flow of particles in a conical hopper. The values and fluctuation of dynamic pressure acting on the wall during the flow of particles in a bin-hopper system were estimated and the generation mechanism of over pressure during flowing of particles was also presented on the basis of the model.