We have studied the effect of TiAl alloy shocked by the laser shock processing (LSP). When the high amplitude shock waves introduced by high energy laser exceed its dynamic yield strength, the mechanical deformation will occur in the shocked material, which will achieve the aim of surface strengthening. By changing the energy of laser and peening times, we get the results of surface roughness and micro-hardness of the work-piece. The results show that with the improvement of peening times and laser energy, the surface roughness and micro-hardness are increased. The microscopic mechanism of peened materials is also investigated in this paper. Compared with un-peened ones, it can be seen that the laser shock peening can effectively improve surface of the dislocation density. When an obstruction impedes dislocation lines (DLs) motion, which will form dislocation tangles (DTs). Accumulation of dislocations is hampered by grain boundary, and forms dislocation walls (DDWs). The transformation of DTs and DDWs into sub-grain boundaries can prepare for grain refinement. The analysis of the mechanism is introduced by laser shock processing, which reveales that dislocation density is the essence of material surface mechanical properties.