The process of ultrasonic shot peening has been studied from two aspects: (a) a 3D numerical model of shot motion in the peening chamber based on the theory of granular gases, (b) an experimental setup developed for measuring shot velocity distribution in the chamber and impact locations on the peened surface. The aim of such study is to propose an experimental method providing shot trajectories in order to validate the 3D model for the process parameter optimization, used for example in the aeronautic industry. The presented results illustrate the value of the model in the understanding and mastering of the process, as well as its usefulness, on one hand for the design of peening chambers, and on the other hand for a better definition of numerical models that help to predict residual stresses generated in the peened material.