A research project is underway to apply the Acoustic Emission (AE) method to establish a non-destructive, non-opening, in-service inspection of high-pressure hydrogen Type 2 accumulators for hydrogen stations. The objective is to prevent hydrogen leakage due to fatigue crack initiation, propagation, and penetration in the steel liner of the accumulator caused by cyclic pressure loading. In this study, the relationship between fatigue crack initiation/growth and AE wave generation behavior is evaluated using a plate-type specimen that simulates the low-alloy steel liner of a pressure accumulator. As a result, AE generation is considered to capture the transition of a crack from Stage I to Stage II, and the usefulness of applying the AE method for in-service inspection of high-pressure hydrogen Type 2 accumulators is demonstrated.