Peening technology is a cold working processing in which peening mediums impinge on a part to improve fatigue life or form a desired shape. The peening medium can be spherical shot, hammer or needle, etc. The shape of the peening medium varies due to processing technology and loading deformation. This paper aims to investigate the effect of peening medium shape on peening results. The peening medium head is assumed to be ellipsoidal and its shape is controlled by aspect ratio. An analytical model of ellipsoid impact response is established based on the expanding cavity model. From the solution of the analytical model, the evolution of shot velocity, indentation size, plastic layer depth, shot deformation and contact pressure are obtained. Finite element simulations are carried out to study the impact results of different ellipsoids , which are verified by peening experiments. The analytical, numerical and experimentally measured indentation sizes are in good agreement. The effects of sharp peening medium and blunt peening medium are compared on indentation geometry, plastic zone size and residual stress field. It is concluded that shallow dimple and thick strengthening layer can be obtained by using blunt peening mediums with high kinetic energy.