Electrocatalytic water splitting is recognized as quite a promising protocol for the renewable hydrogen energy production, and significant effort has been devoted to the design of high‐performance electrocatalysts that can efficiently alleviate the critical issue of fossil fuel scarcity. However, the vast majority of traditional design strategies restrictedly focus on the pristine electrocatalyst structure and ultimate performance results, which may lead to the incorrect or even opposite understanding of catalytic structure–performance correlations. With the burgeoning development of in situ techniques, the dynamic service behaviors of electrocatalysts during water splitting have been growingly investigated from enriched perspectives, only by which can the life‐time dynamic structure–performance correlations be established. Herein, to shed new light on the next‐stage development of in situ investigations for water splitting electrocatalysts, a series of dynamic service behavior that existed in water splitting process and highlight their key role for understanding the life‐time dynamic structure–performance correlations is comprehensively summarized. Besides, a wide variety of in situ techniques are systematically dissected in terms of their functional features, advantages, and limitations. Critical challenges and prospects are also discussed for establishing the life‐time dynamic structure–performance correlations of water splitting electrocatalysts.