[en] A hemispherical model and the Number 4 pressure vessel model were used as samples to determine the usefulness of acoustic emission (AE) method in tracing internal pressure fatigue crack propagation in light water reactor pressure vessels. In the hemispherical model, artificial notches were fabricated at the top. In the Number 4 pressure vessel model, two types of artificial notches were fabricated at the points of origin of the maximum stress (corners of the inner surface of the nozzles) in four nozzles with different shapes which were mounted on the model itself. The AE method was used to investigate the process of crack initiation and propagation from these artificial notches by means of repeated loading with internal pressure. Useful data concerning the properties of AE and the points of origin of AE (positional tracking) were obtained when cracks were initiated and propagated in structures having complex shapes. Smek gages and crack gages mounted on the nozzle corners to investigate the track initiation and propagation behavior were used simultaneously with AE methods. It was established that there is a close connection between them