In order to evaluate the fatigue life of welded structure more accurately, a new method was presented to predict the total fatigue life, which combined critical distance method and fracture mechanics theory. The distribution law of welding residual stress was obtained through the 3D finite element dynamic simulation of welding process. The local stress-life curve was predicted by the critical distance theory, and the prediction method of fatigue crack initiation life was given. During the crack growth stage, the stress intensity factor of the crack was corrected according to the transient crack size, the residual stress intensity factor was solved by using the weight function method, and the fatigue crack propagation life was calculated by combining the Forman formula. Compared fatigue test results of welded cross joints with predicted total life, it is found that they are in good agreement. Under different load levels, with different proportion of crack initiation and propagation life to total fatigue life, the existence of residual stress all has an adverse effect on the fatigue life at both stages.