Electrocatalytic hydrogenation (ECH) reaction offers a sustainable route for upgrading renewable feedstocks using water as the hydrogen source. However, its efficiency and selectivity are often limited by the complex interplay between hetero-intermediates, such as water-derived hydrogen species and diverse hydrogen acceptors, making it difficult to control reaction pathways and mechanisms. This review aims to provide an insight into ECH reactions. Three representative models, including coupling, competitive, and promotion, are introduced to capture the dominant interaction modes among intermediates at key steps during reaction. By focusing on how these interactions shape pathway evolution and product selectivity, the framework provides mechanistic clarity for interpreting complex ECH systems and understanding performance regulation. An outlook on the current challenges and promising opportunities in this field is also discussed. This review offers a constructive perspective for understanding mechanism and performance regulation of efficient ECH reactions.