Abstract: Based on the mechanical characteristics of TC4 titanium alloy welded joints applied in ships and naval vessels etc,this paper modified the existing non-linear continuum damage model according to the fourth strength theory,and proposed a new non-linear continuum damage model that was better in conformity with engineering practice. The model parameters were estimated according to the fatigue experimental data. Then the correctness of the modified damage model was carried out according to the observation and analysis of the fatigue-unloaded specimens by SEM. By comparing the modified non-linear damage model, the linear damage model and experimental data,the results show that the linear damage model was relatively conservative in estimating the fatigue life with medium or low load,but the modified non-linear damage model had higher accuracy and agreed well with the experimental data.