The fatigue life of titanium alloy materials is composed of fatigue crack initiation life and crack propagation life. The crack initiation life of smooth samples can account for 80% of the entire fatigue life. Hydrogen has an important influence on the fatigue behavior of titanium alloys, especially the fatigue crack initiation mechanism. The researchers used variable cross-section thin plate samples to study the effect of four hydrogen contents on the fatigue life of Ti-4Al-2V titanium alloys. When the tensile fatigue load Δσ is greater than 550 MPa, the fatigue life of the material containing 116-280 wppm of hydrogen is higher than that of the material containing natural hydrogen. At a larger Δσ, the hydrogen content changes within the range of 116-280wppm and has little effect on the life of Ti-4Al-2V. For the 280wppm sample, the larger Δσ is dominated by initiating edge cracks, and the smaller Δσ tends to initiate cracks at the grain boundary hydride position. The researchers believe that the solid solution of hydrogen in the material leads to further softening of the resident slip zone (PSB), and the hydride’s blocking effect on the PSB causes the hydride to separate from the matrix and become a source of cracks, which causes the fatigue life of the hydrogen-filled sample to be reduced. The reason is that the Ti-4Al-2V material containing 280wppm of hydrogen will re-dissolve the hydride when the fatigue load is low, and hydrogen atoms will gather to the tip of the main crack and the hydride will be precipitated by stress induction, which will reduce the crack propagation life.