The invention discloses a method for predicting a fatigue crack propagation threshold value of a welded joint. The method comprises the following steps: firstly, carrying out high-cycle fatigue test on a sample; then, observing and measuring the area of a fatigue crack initiation region and the long/short semiaxis of an air hole in a fracture surface under a scanning electron microscope or a three-dimensional white light interference profilometer according to the condition of an inner air hole crack initiation source in the sample; calculating a stress intensity factor range corresponding to a high-cycle fatigue crack initiation region; and eliminating the influence from the shape of the welded air hole by using a double logarithmic fitting method to finally achieve the aim of predicting the fatigue crack propagation threshold value R=0 of the welded joint. Compared with traditional research, the method is suitable for the welded joint with the air hole as the high-cycle fatigue crack initiation source and widens the application range of the existing achievements.