Abstract: 【Objective】 This research aims to study the effect of defoliantion spraying time on cotton defoliation and the yield of fruit branches at different positions in the hope of screening out the appropriate defoliant spraying time and providing a theoretical basis for increasing yield and quality. 【Method】 The five main varieties of northern Xinjiang were taken as materials, three spraying treatments were set up during the boll-out period, with boll-out rate of 10%-20% (T₁), boll-out rate of 30%-50% (T₂), and boll-out rate of 70%-80% (T₃), with spraying clean water as the control (CK) to explore the effect of defoliant treatment on cotton defoliation rate, boll spit rate, yield and yield components. 【Results】 The results showed that Miaobao 21 and Xinluzao 37 had the best defoliation effect at T₃; Nongda 1, Guoxin 73 and C₁ had the best defoliation effect at T₂.Defoliant treatment had little effect on the boll-out rate of Miaobao 21 and Nongda 1, and the boll-out rate was about 85%.It had a greater impact on the boll release rate of Guoxin 73 and C₁, and Miaobao 21 T₂ was significantly higher than those of T₁.Nongda 1, Guoxin No.73 and Xinluzao 37 T₁ boil-off rate was higher than those of other treatments.Nongda 1, Guoxin 73 and Xinluzao 37 T₁ boil-off rate was higher than those of other treatments.The highest T₃ spitting rate was observed between the C₁ treatments.With the spraying time of the defoliant, the natural flocculation increased (T₃>T₂>T₁), and the increase of the flocculation of each variety and treatment gradually decreased (T₁>T₂>T₃).During the T₂ period of Miaobao 21 and Nongda 1, the yield of seed cotton and lint increased significantly, but the lint score was relatively low, and the CK lint score was the highest.C₁ clothing score was significantly higher than that of T₁ during T₂. Different varieties, treatments and positions of fruit branches had interactive effects on yield, lint percentage and boll weight. 【Conclusion】 The study has found that Miaobao 21, Nongda 1, Guoxin 73, and C₁ have better defoliation effects at T₂, better flocculation rate, relatively higher seed cotton yield and lint yield, and lower lint; the defoliation of Xinluzao 37 at T₃ is the best, the flocculation rate is higher, the yield is the highest, and the lint and boll weight are the highest.