Alkaline water splitting, especially anion-exchange-membrane based water electrolysis, is an attractive way for low-cost and scalable H 2 production. Green electricity-driven alkaline water electrolysis requires that highly-efficient electrocatalysts be developed to further decrease the barriers of two half reactions - the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Various strategies have been exploited to date, among which atomic heterointerface engineering is the most promising strategy to overcome the intrinsic activity limitation of electrocatalysts. In this review, we thoroughly summarize the recent progress of atomic heterointerface engineering to improve the activity of electrocatalysts. The origin and rationale of the sluggish kinetics of the alkaline HER and OER are first introduced. Subsequently, the synergistic effects (ensemble effect and electron effect) of atomic heterointerface engineering to overcome the activity limitation are elaborated, in which the ensemble effect is helpful in optimizing the reaction pathways with enhanced reaction kinetics by creating a favorable heterointerface and the electron effect can balance the adsorption energies of reaction intermediates by coupling their electronic configurations. And then the rational design of the targeted electrocatalysts is concluded based on the heterointerface constituents and characteristics. At the end, some outlooks about the future development direction for optimizing and maximizing the interfacial active sites in the electrocatalysts are proposed. This review summarizes the recent progress of atomic heterointerface engineering to overcome the activity limitation of electrocatalysts for water splitting and elaborates its electron effect and ensemble effect, etc.