Abstract: Solide carbon source denitrification technology is a pivotal strategy for treating low carbon-to-nitrogen (C/N) wastewater, and the important factor affecting the efficiency of biological denitrification is the characteristics of the carbon source. The advantages and application prospects of various types of solid carbon sources, including synthetic biodegradable polymers, natural cellulosic substances, and mixed solid carbon sources, were compared and elucidated, aiming at the unclear principle of their application in nitrogen removal. Detailed analysis was conducted on the influences of physical and chemical properties of carbon sources (such as synthetic substances, carbon released composition, and surface characteristics) and the dosing sites, etc. on the biological denitrification process. The results indicated that the carbon release and its subsequent utilization rate by denitrifying microorganisms were crucial determinants of denitrification efficiency. By optimizing material composition and mixing methods to modify the material characteristics, carbon release could be maximized and the released components could be better utilized by denitrifying microorganisms. It was proposed that the future solid carbon source field should focus on enhancing carbon release capabilities and denitrification rates through advancements in the synthesis of carbon sources and the elucidation of electron transfer mechanisms, to deeply develop and promote novel solid carbon sources.