Abstract: 【Objective】 The aim of this study is to provide a theoretical basis for selecting early-maturing machine-picked cotton varieties with excellent defoliation effect. 【Method】 Multiple linear regression analyses, correlation analysis, and other comparisons were executed on experimental data using EXCEL 2007, ORIGIN and SPSS21.0 software. Phenotypic traits of different types of leaves and various individual plants under different canopy conditions were studied. The relationship between the leaf shedding rate of different types of leaves was clarified by regression analysis, and the important factors affecting the leaf shedding rate of a single plant were found. 【Results】 The abscission rate of main stem leaf, fruit spur leaf and leafy shoot leaf was significantly different among different cultivars.There was a significant negative correlation between the number of main stem leaf and abscission rate, but no significant correlation between the number of other types of leaves and leaf phenotypic traits and abscission rate.The main stem leaf had the fastest response to defoliating agent, while the leaf of leafy shoot had the slowest response.The peak of defoliation of fruit spur leaf appeared in the middle defoliation, and the peak of defoliation of main stem leaf and the leaf of leafy shoot appeared in the late defoliation. The defoliation rate of main stem leaf was stable, and the fitting regression equation was Y=0.101-0.804X₁-0.663X₂ (R²=0.740, P < 0.01).The defoliation rate of fruit spur leaf showed a "slow-fast-slow" trend, and the fitting regression equation was Y=0.110-0.686X₁-0.789 X₂(R²=0.887, P < 0.01). The leaf of leafy shoot could not be fitted to the equation. 【Conclusion】 The defoliation rate per plant is negatively correlated with the number of leaves in the main stem. The leaf of leafy shoot is important factors in defoliation effect.The defoliation rate of the main stem leaf and the leaf of fruit spur was greatly affected by the characteristics of the variety itself, which had predictability and could be fitted with the equation.The defoliation rate of the leaf of leafy shoot is not only affected by the variety itself, but also by other factors, so the equation cannot be fitted.