Laser shock hardening is a well-known method for prolonging the fatigue life of metals components by introducing near-surface compressive residual stresses. The surface acoustic wave can disperse when the material properties of near-surface change. The near-surface properties, such as elastic properties, residual stresses, can be analyzed by the phase velocity dispersion. An experiment method is presented to detect laser surface acoustic wave (SAW) of Al alloy by laser shock. Based on the advantage of broad bandwidth generation and detection, the experiment use laser excitating and polyvinylindene fluoride (PVDF) as transducer. The SAW signals in aluminum alloy material under different conditions by laser shock hardening were detected. The signals spectrum and phase velocity dispersive curves were obtained and analyzed. The SAW velocity dispersion is mainly caused by the near-surface grain reorientation and the increasing of dislocation density.