Shot-peening is a surface treatment widely used in the industry to improve fatigue life of mechanical components by introducing compressive residual stresses. Ultrasonic shot-peening is a recent development of this process. While the classical shot-peening process uses pneumatic energy to project the shots, ultrasonic peening uses high-power ultrasounds. This energy source allows the use of larger shots projected at lower velocity as compared to classical shot-peening. This work aims at studying the mechanical response (restitution coefficient, residual stress field) of a surface impacted by a shot at low velocity using the finite element method and experimental analysis. This paper presents the simulation of a single elastic steel shot normally impacting an Aluminum alloy plate considered to exhibit a linear-elastic behavior and non-linear isotropic work hardening characteristics. The numerical simulations are carried out for different impact velocities in order to take into account the heterogeneous shot velocity field observed in an ultrasonic shot-peening chamber. We compare the simulated rebound energy and the indentation profiles obtained for different impact velocities to experimental results. The simulated residual stress field topology shows a strong dependence on the shot velocity. While numerical results obtained at high impact energy agree well with literature results, the residual stress distribution simulated for low impact energies shows a tensile layer below the impacted area. The restitution coefficients and the indentation profiles compare well with the experiments.