Abstract: To investigate the effect of DPC chemical treatment on agronomic traits, yield and quality of machine-harvested cotton in the Yellow River valley of China, and clarify the reasonable control period and the application amount of DPC, a new machine-harvested cotton variety Hengmian HD008 was used as the test material, and 3 different DPC treatments were set. The results showed that DPC significantly reduced plant height and branch length, reduced branch angle and leaf area, so the rational control could effectively shape the ideal plant type of machine-harvested cotton. DPC had significant effects on yield and yield components, the proper amount of DPC could increase the number of pre- hot seasonal boll and autumn boll, thus to increase the total boll number, the boll weight and the seed index, but the lint percentage decreased, and the proper amount of DPC could increase the yield. DPC significantly increased the fracture ratio of the fiber, and proper control could improve the uniformity of fibers, but other indexes had no significant change. According to the requirements of machine harvest to the agronomic traits of cotton and the growth characteristics of cotton, chemical control could begin after cotton floral bud emergence, once about every 10 days, and the spraying amount could be controlled according to the growth amount of the main stem. The daily growth amount of plant height should be controlled at 1.5-1.8 cm, and the plant height should be within 75-90 cm.