Due to the ability of cocatalysts to form heterojunctions on the surface in contact with g?C₃N₄, promoting the migration of photo generated electrons and enhancing the photocatalytic performance of g?C₃N₄, the introduction of cocatalysts plays a significant role in improving the photocatalytic activity of g?C₃N₄. Common co?catalysts can be broadly categorized into three groups: transition metal?based cocatalysts (non?precious?metal co?catalysts), precious metal based co?catalysts, and non?metal cocatalysts. Among them, transition metal?based cocatalysts have attracted widespread attention due to their low cost and strong ability to capture electrons. This article focuses on the composite methods, mechanisms of action, and their effects on the photocatalytic performance of various transition metal based cocatalysts (such as metal oxides, sulfides, phosphides, etc.) with g?C₃N₄, aiming to provide comprehensive theoretical and practical guidance for the design and development of efficient g?C₃N₄ based photocatalysts.