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Laser peening (LP) treatment with different power densities was used to improve the vibration fatigue resistance of hydrogenated TC4 titanium alloy. Compressive residual stress (CRS), micro-hardness and micro-structure of hydrogenated LPed specimens were firstly measured. Vibration fatigue test was then carried out to compare the fatigue life and fractures of LPed and non-LPed hydrogenated specimens. It was found that LP-induced high level CRS suppressed the permeation of hydrogen atoms through material surface, which may reduce the hydrogen embrittlement sensitivity. The CRS also prohibited the fatigue crack initiation and propagation by increasing the fatigue limit and crack propagation threshold of hydrogenated specimen. Grain morphologies of α phase and β phase were refined after LP. Beneficial crystal defects inside the α phase and β phase tangled more free hydrogen atoms, which was believed to be crucial factors to inhibit the generation of initial hydrogen-induced crack. Fracture morphologies further confirmed that LP changed the location of fatigue crack initiation (FCI) and slowed down the fatigue crack growth (FCG) rate of hydrogenated specimens. Finally, a strengthening mechanism of LP on the vibration fatigue resistance of hydrogenated specimen was proposed.