The effects of massive laser shock peening (LSP) treatment with different pulse energies on surface roughness and microstructural evolution in the surface layer of AISI304 stainless steel were investigated. The deformation-induced grain subdivision processes under two LSP treatment conditions of 3 and 6J pulse energies were characterized and presented, respectively. Subsequently, EBSD characterization was conducted to analyze the peaks of misorientation angle for as-machined sample and LSPed samples with different pulse energies. Furthermore, a novel MT–MT intersection with four directions was found for the first time in the plastic deformation layer of AISI304 stainless steel, and the generation mechanism was completely presented according to the inherited crystal structure of austenite stainless steel. The formation process of the surface roughness and the formed microstructure subjected to massive LSP impact treatment with different pulse energies were compared and revealed.