Provided is an ultrasonic assisted laser peening method for obtaining an ultrafine grain surface layer, comprising: using ultrasonic vibration waves emitted by an ultrasonic transducer to induce high-frequency vibration waves on a metal surface layer, and using laser shock waves and the ultrasonic vibration waves to jointly prepare a metal material having the ultrafine grain surface layer. The high-frequency vibration waves induced by the ultrasonic vibration waves may cause the atomic lattice to be periodically dense and loose, so as to promote rapid transition of microscopic structures, such as dislocation cells and dislocation walls, to a low energy state during the propagation of the laser shock waves, and to promote the formation of sub-grain boundaries and large angle grain boundaries, effectively increasing the dynamic recrystallization behavior induced by the laser peening, thereby improving the grain refinement ability of the traditional laser peening technology, obtaining a metal material having an ultrafine grain surface layer, and improving the fatigue strength and fracture toughness of a metal part; in addition, this technology has the characteristics of low pollution, low cost and high efficiency.
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