<p>Modifying the top-layer surface microstructures represents a promising strategy for surface strengthening and is increasingly utilized in metal surface engineering. Here, we achieved nearly nondestructive surface reinforcement and gradient structuring of aluminum alloy using a low-energy femtosecond laser peening technique. Gradient micro-nano structures were formed after femtosecond laser peening treatment including gradient grains in size from hundreds of nanometers to a few micrometers, massive subgrain boundaries, various dislocation patterns, accompanied with more than one-fold elevated surface hardness and approximately unchanged surface evenness. The use of low pulse energy effectively suppresses thermal melting and collateral damage, ensuring high surface integrity. Atomistic simulations of defect evolution, such as dislocation propagation, multiplication, interactions with voids, and grain boundaries, demonstrate that ultrafast shockwaves facilitate the development of micro-nano structures, thereby enhancing the deformation capacity of the lattice and significantly improving the mechanical properties of the laser-treated surface. This advancement in metallic surface engineering techniques offers vast potential for manufacturing advanced metal materials with exceptional mechanical performance.</p> Graphical Abstract <p></p>