The distribution characteristics of residual stress field along the surface and depth directions are investigated by numerical simulation when laser shocks titanium alloy parts with different thicknesses. The reflection of shock wave among different planes is investigated by dynamic analyses. The results show that, when the thickness increases but other parameters are kept constant, the front residual stress increases while the reverse residual stress increases first and then decreases. As for the front micro-hardness, it reaches the maximum at 440.2 HV when the specimen thickness is 4 mm, in contrast, the reverse micro-hardness reaches the maximum at 416.1 HV when the specimen thickness is 2 mm. The tensile and compressional waves are generated when the shock wave interacts with the acoustic impedance interface, which have obvious influences on the residual stress field distribution.