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[Objective] The present paper aimed to explore the changing law of twig and leaf size relationship in the vertical structure of woody plants in the dry-hot valley of northwest Guangxi, and provide a theoretical basis for plant protection and vegetation restoration in the dry-hot valley of northwest Guangxi. [Method] The natural secondary forest community in Yachang Forest Farm in the dry-hot valley of northwest Guangxi was studied by using one-way ANOVA, standardized principal axis estimation and correlation analysis to analyze the size difference, allometric growth relationship and correlation relationship among twigs and leaves in different forest layers. [Result] There were significant differences in the traits of most twigs and leaves in different forest layers (P<0.05, the same as below). With the increase of forest layer, twig fresh weight, twig dry weight, twig diameter, total leaf area, leaf fresh weight, leaf dry weight and leaf dry matter content showed an increasing trend, while twig relative water content, branching intensity, individual leaf area, leaf relative water content and specific leaf area showed a decreasing trend. There was a significant positive allometric growth relationship between twig cross-sectional area and total leaf area, and a significant negative allometric growth relationship between twig cross-sectional area and branching density in different forest layers, with a common slope and significant differences in the intercept of the regression equation, indicating that vertical structure changes do not change the ecological tradeoff between branch size, branch number and leaf area, but significantly changed the proportion of resource allocation for twig and leaf traits. Tall forest plants supported fewer twigs per unit area and more total leaf area. Correlation analysis showed that vertical structure changes have a significant impact on plant twig and leaf traits, and the correlation between plant twig and leaf traits was closer in lower and middle forest than in upper forest. [Conclusion] Vertical structural changes do not significantly affect the ecological tradeoffs between leafy traits in woody plants, but significantly affect the biomass configuration of branches and leaves. The upper woody plants per unit area have a larger leaf area, while the lower woody plants support a larger number of branches, which is an ecological strategy adopted by woody plants in the dry-hot valley of northwest Guangxi. [ABSTRACT FROM AUTHOR]