Global warming has a strong effect on forests, an important part of the terrestrial ecosystem, because temperature change easily influences photosynthesis. At present, most studies about global warming's effects on photosynthesis are concentrated in high latitudes and alpine regions, with few reports from subtropical forests. Cunninghamia lanceolata is the main species used in afforestation in subtropical China. To clarify how C. lanceolata growth and photosynthesis respond to future global warming, we conducted a soil warming (cable heating, +4℃) experiment at Chenda observation point in the Sanming Research Station of Forest Ecosystem and Global Change, Fujian Province. We estimated growth variables (tree height and ground diameter), variation in photosynthesis, soil inorganic nitrogen (N) content, leaf N content, chlorophyll content (Chl), and non-structural carbohydrates (NSC). The results showed that under soil warming, net photosynthetic rate (P_n) and water use efficiency (WUE) of C. lanceolata seedlings increased by 71.4% and 51.3%, respectively. Additionally, stomatal conductance (G_s), transpiration rate (T_r), and intercellular carbon dioxide concentration (C_i) were maintained at high levels. Increasing soil temperature also promoted the mineralization of soil organic N, elevating available N for plant absorption and use. These changes caused significant increase in N content of C. lanceolata leaves. Because N is a major chlorophyll component, we also observed a notable increase in total Chl a, Chl b, and Chl by 76.3%, 55.8%, and 68.7%, respectively. The ratio of Chl a to b also increased. Soil warming did not significantly alter tree height, ground diameter, and leaf NSC content of C. lanceolata seedlings. In summary, soil warming improves C. lanceolata photosynthetic efficiency through altering stomatal conductance sensitivity and promoting Chl synthesis in leaves, thus increasing CO₂ absorption and light capturing ability. Simultaneously, warming-induced elevation in rhizosphere temperature may significantly increase respiration rate, accelerating carbohydrate consumption. Therefore, even after three months of soil warming, leaf NSC content and sapling growth did not significantly change. This experiment demonstrates that C. lanceolata growth and photosynthetic capacity adapts to global warming, providing a reference for predicting potential carbon sequestration of subtropical plantations in China.