Abstract: 【Objective】 To study the development and quality of cotton boll period after sowing in cotton field under drip irrigation based on the different sowing dates and analyze the relationship between cotton boll development and temperature in cotton top after sowing in stages so as to provide theoretical basis for determining the date of sowing and the date of spraying defoliant. 【Method】 Field experiments were carried out at Wulanwusu agricultural meteorological test station between years 2016 and 2017. With normal temperature sowing time as control and setting up 3-4 sowing dates, the cotton boll weight and cotton fiber quality were measured. The weight and quality of cotton boll and bell during the development of cotton bolls at the top of different sowing dates were studied. The mechanism of quality formation provided theoretical basis for determining sowing and improving fiber quality of cotton under mulch drip irrigation. 【Result】 Under the conditions of April 8th (early sowing), the single boll weight of cotton boll was 0.79%-11.02% higher than the those at other sowing dates, the flowering boll stage was 3-10 days earlier, the cotton fiber length was 1.05%-3.86% higher, the strength was 2.00%-9.49% higher, the uniformity was 0.59%-2.03% higher, and the value of the micronaire was 0.41%-13.76% higher. 【Conclusion】 under the condition of daily temperature of 23.70-23.86 ℃, the cotton boll growth in the top of cotton in April 8th (early sowing) conditions, the period of flower and boll is earlier, the development time of cotton top boll ring is shortened, and the weight of the single bell is larger and the fiber quality of cotton is higher. Among them, daily average temperature has the greatest influence on cotton boll weight and fiber quality, and could be used as an important index to measure cotton boll development at the top of cotton. In April 29 th (late sowing), the cotton boll development is shortened and fiber development is affected by the minimum temperature, which is not conducive to the formation of high strength fiber and high quality cotton boll.