Abstract: To investigate the effects of laser shock peening (LSP) on the microstructure, residual stress, and fatigue performance of wire and arc additive manufactured (WAAM) TC17 titanium alloy, the WAAM TC17 titanium alloy was treated by LSP. The results indicate that the WAAM TC17 titanium alloy exhibits a typical basket-weave structure. After LSP treatment, significant plastic deformation occurs in the surface layer of the material, forming a high-density dislocation structure mainly characterized by dislocation entanglement, accompanied by a phase transformation from a hexagonal close packed (HCP) structure to a face centered cubic (FCC) structure. As the plastic deformation continues, the stress concentration caused by the obstruction of dislocation movement gradually accumulates, eventually activating a large number of mechanical twins. The synergistic interaction between dislocation proliferation and twinning achieves grain refinement, reducing the average area of the α phase from 3.7 μm² to 3.1 μm². An affected layer with a depth of approximately 0.9 mm is formed by LSP in the surface layer of the specimen, and a maximum residual compressive stress of 586 MPa is induced, increasing the microhardness from 406 HV to 468 HV. Based on the synergistic strengthening effect of grain refinement and residual compressive stress, the high-cycle fatigue performance of the WAAM TC17 titanium alloy is significantly improved, and the fatigue life at a stress level of 610 MPa is increased to more than 2.9 times.