The tobacco-rice rotation area in Hunan Province is one of China’s most important and representative tobacco-producing regions. Yongzhou is a key tobacco-rice rotation area in Hunan. However, current challenges such as low phosphorus utilization efficiency in soil and insufficient sweetness and declining quality of tobacco leaves have emerged. Selecting appropriate phosphorus fertilizer types has become an effective solution to address these issues. In order to explore suitable phosphorus fertilizer types for Yongzhou tobacco-growing areas, this study conducted field plot experiments using ammonium dihydrogen phosphate (P1), calcium superphosphate (P2), and their compound mixtures with humic acid (P1H, P2H), investigated the effects of phosphorus fertilizer types on agronomic traits, photosynthesis, carbon metabolism enzyme activities, and sugar accumulation in tobacco leaves during different growth stages. Results showed that both P1 and P2 applications improved agronomic traits at rosette, vigorous, and maturation stages. P1 demonstrated better effects during the vigorous growth stage, while P2 showed superior performance at rosette and maturation stages. P2 significantly enhanced transpiration rate, photosynthetic rate, stomatal conductance, and intercellular CO₂concentration during the vigorous growth stage, with greater increases than P1. Both fertilizers significantly promoted the accumulation of reducing sugars and sucrose during the vigorous growth, with P2 additionally reducing starch content. P2 demonstrated better enhancement of sucrose phosphate synthase activity compared to P1, whereas P1 significantly inhibited the activity of ADP-glucose pyrophosphorylase (a key starch synthesis enzyme). Phosphorus application increased the contents of reducing sugars, total sugars, and sugar-to-alkaloid ratio in the post-cured leaves, with more pronounced improvements from P2. Overall, P2 application showed better comprehensive effects than P1. Humic acid effectively enhanced P1’s performance in improving agronomic traits, photosynthetic capacity, sugar synthesis/accumulation, and coordinating the chemical composition of leaves. For tobacco fields in southern Hunan's Yongzhou region, the strategy of combining monoammonium phosphate with humic acid is recommended, which can effectively improve tobacco carbon metabolism efficiency, promote sugar accumulation, and enhance leaf quality.