Laser shock processing (LSP), also known as laser peening, is a novel surface strengthening treatment technology, which is capable of introducing residual compressive stress, improving performance of fatigue strength and micro-hardness. With its preferable reinforcement effect, strong controllability and outstanding adaptability, LSP plays an irreplaceable role in improving the service life of key components. The evolution of microstructure in the plastic deformation layer of Ti834 alloy subjected to LSP impacts were investigated by means of transmission electron microscopy (TEM) observations, and the microstructure evolution model in the surface layer and depth direction was established. The results indicate that numerous dislocations are generated in the plastic deformation layer of Ti834 alloy subjected to LSP, and the plastic deformation becomes more intense and the dislocation density further increases as the number of impacts increases. Typical microstructure features due to decreasing strain rates can be observed along the depth direction, including mechanical twins (MTs), dense density dislocation walls (DDWs), dislocation tangles (DTs), dislocation arrays (DAs) and dislocation lines (DLs).