Abstract: In order to study effect of laser shock processing(LSP) on the fatigue life of fillet structures under different stress levels (the maximum stress during fatigue test), TC4-DT titanium alloy samples were subjected to laser shock processing, and then tensile stress test was carried out. The stress levels were 385MPa and 423MPa respectively, and the stress ratio r was 0.1. The fatigue fracture was analyzed by means of a scanning electron microscope (SEM). The results show that after laser shock processing, the fatigue crack initiation is moved from the fillet surface to the inside, the width of fatigue striation decreases, and the fatigue life of fillet structure is improved. With the increase of stress level, the gain of the fatigue life of the fillet treated by laser shock processing is reduced. When the stress level increases from 385MPa to 423MPa, the fatigue life gain of fillet structure decreases from 246.2% to 111.8%. After LSP, the surface of the fillet has a certain degree of compressive stress, and the fatigue life is improved. However, with the increase of the stress level, thefatigue life gain of the fillet structure is reduced.This result has guiding significance for the study on suppressing fatigue crack initiation by strengthening weak region.