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Surface grain refinement by severe plastic deformation is a relatively new process aimed to enhance mechanical material properties. Among the technological processes used with this aim, shot peening (SP) is one of the most promising, both in terms of costs and as concern the possible production rate. In this study Al7075-T6 bars have been shot peened with parameters (shot speed and treatment duration) much different from those of conventional shot peening. Residual stress state and microstructure gradient have been observed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), optical microscopy (OM) and nano indentation tester. Formation of a nanostructured layer on top surface of the specimens was confirmed by OM and TEM and also XRD measurements. XRD results show significant depth affected both in terms of residual stress and FWHM. Measurements also indicate of notable improvements in cases of hardness and elastic modulus in comparison with untreated material. A finite element (FE) model is developed in order to obtain a tool for predicting the effects of treatment parameters on final state of the surface and to interpret the experimental evidence. A detailed approach is chosen for simulating multiple high energy impacts on a 3-dimensional model: the results are in good agreement with experimental evidence.