Non-structural carbohydrates (NSCs) are important energy sources in the process of plant growth and metabolism. In this paper, we conducted field-based experiment with nitrogen (N) and phosphorus (P) addition, to explore the seasonal changes of leaf NSCs in different forest layers and its response to N and P additions in a secondary tropical forest in south China. Leaf samples were conducted in January, April, July, and October 2019. The results showed that:1) There were significantly interspecific differences on the leaf NSCs. Phosphorus addition had a significant impact on starch and NSCs contents, and the interactions between species and P addition significantly affected the starch content. 2) Leaf NSCs of Syzygium bullockii and Uvaria microcarpa were sensitive to N addition, while those of Syzygium levinei and Carallia brachiate were sensitive to P addition, and N and P co-addition (+NP) had the best synergistic effect on leaf NSCs. 3) There were significantly seasonal changes on leaf NSCs, and the interaction between seasons and forest layers significantly affected soluble sugar and NSCs content. 4) The responses of plants in different forest layers to N and P addition were different. N and P additions increased the leaf soluble sugar content in the understory and decreased those in the overstory plants. In dry season, N addition increased the leaf starch contents in the understory and decreased in the overstory species. However, P addition had the opposite effect. In wet season, N and P additions increased the starch content of plant leaves in understory and overstory. 5) Leaf NSCs content in overstory was higher than that in understory. The leaf NSCs content and soluble sugar/starch ratio of understory plants were higher in the dry season than those in wet season. Therefore, the variation of NSCs in different plant leaves reflects the carbon (C) utilization strategies, and the change of NSCs content in response to N and P addition can reflect the dynamic changes of C supply and consumption during the growth and development of tropical forest plants, which provides scientific basis for exploring C utilization strategies and coexistence mechanisms of plants in secondary tropical forest.