This paper aims to quantitatively elucidate the degradation phenomena occurring in a proton exchange membrane (PEM) water electrolysis cell under variable load fluctuations. By varying the accelerated stress test conditions, the electrochemical characteristics, such as I–V polarization, cyclic voltammetry, and electrochemical impedance spectroscopy, were analyzed after 0, 22, 33, and 50 h of operation. The primary cause of performance degradation was identified as repeated exposure to open-circuit voltage. Applying a small minimum current density (e.g., 0.1 A cm⁻²) was confirmed to be an effective strategy for mitigating this degradation. These findings provide a basis for establishing an optimal load-fluctuation protocol for PEM electrolysis stack.