This paper presents a numerical study of the deagglomeration mechanisms of fine powders subjected to particle-wall impaction based on the discrete element method (DEM). The agglomerates of fine powders down to 5μm in size were first formed under the centripetal force, and then collide with a wall at various impact velocities and angles. The time evolution of agglomerate structures and stress are analysed. The deagglomeration efficiency is described by the proposed 80% passing size parameter. By varying the agglomerate properties, and impact velocity and impact angle, we investigate how these parameters affect the deagglomeration and apply the findings to the optimum control of deagglomeration process. The breakage mechanism was found to be very different from that of agglomerate reported previously. There is extensive deformation takes place which resembles the agglomerate is very weak. The simulation results identified a critical fatigue value below which the agglomerate did not break. A comparison of impact breakage of different angles showed that large and small angles both have negative effect at the deagglomeration efficiency. The fragment size can be described by the Weibull distribution which is based on the fractional principle of the weakest link in a chain.