Abstract: 【Objective】 To study the effects of defoliants on defoliation, yield and quality of machine-picked cotton in southern Xinjiang. 【Methods】 The 4 machine-picked cotton planting modes were set up, one film six lines K₁(12 cm+64 cm+12 cm+64 cm+12 cm)+64 cm×11 cm; one film three lines K₂(76 cm+76 cm)+76 cm×5.6 cm; one film three lines K₃(76 cm+76 cm)+76 cm×9.5 cm; one film four lines K₄(12 cm+64 cm+12 cm)+64cm×11 cm. during the cotton fluffing period, the effects of defoliation, yield and quality were analyzed under different planting patterns after spraying defoliation ripening agent. 【Results】 There were no significant difference in defoliation rate and fluffing rate in 25 days after spraying defoliation and ripening agent in different planting modes. The K₁ planting mode had the highest yield, and the seed cotton yield was respectively 5.15%, 8.7%, and 4.5% higher than those of the K₂, K₃, and K₄ planting modes in 2020. After spraying the defoliant ripening agent, there was no significant difference in uniformity of length of cotton fiber, specific breaking strength, micronaire, elongation at break, staple fibre index and maturity between different planting patterns. 【Conclusion】 There is no significant difference in defoliation rate and flocculation rate among different planting modes after spraying defoliation and ripening agent. Spraying defoliation and ripening agent has little effect on cotton fiber quality,cotton yield is the highest under the mode of one film six lines.