The standard vibration fatigue specimens, made of TC11 titanium alloy, are treated by laser shock peening (LSP). The high-cycle vibration tests are conducted to verify the reinforcement effect, and the fracture analysis is utilized to analyze the fatigue mechanism of the treated specimens. The strengthening mechanism of fatigue performance is explained by the experiments of microstructure, residual stress and microhardness. The tests results show that the fatigue limit is improved from 483 MPa to 593 MPa by LSP. Fatigue crack of specimens treated by LSP initiates in the subsurface of 0.2-mm depth with a greater flatness area and lots of second-cracks and tight fatigue bands. A layer with nanocrystals is generated on the surface by LSP, and the size of nanocrystal is about 40~80 nm. LSP introduce a great compressive residual stress in the material with a 1-mm thick plastic deformation layer. The residual stress in the surface can reach -591.5 MPa, while the surface hardness is increased by 19%. The combined actions of high structure refinement and high compressive residual stress are the main causes of the fatigue performance improvement, which block fatigue crack initiating and reduce crack growth rate.