The influences of hydrogen charging on microstructure and fatigue lives of electron beam welded TA15 alloys were studied. The microstructure observation shows that hydrogen exists in the alloy in the form of solid solution, and no hydride is formed when the hydrogen content is less than 0.105% (mass fraction). Fatigue life tests show that with the hydrogen content increasing, the fatigue life in the welded joints drops. It is because trace hydrogen decreases the toughness of TA15 alloy and solid-solution hydrogen increases the fatigue crack growth rate. In addition, the hydrogen atoms accelerate the fatigue crack propagation by influencing the behavior of crack tips. The existence of the "colony structures" in the fracture morphology reveals that the martensite packets perform as a unit, and hydrogen has some effects on the martensite packet during the crack propagation.