Abstract: Cotton is one of the most important economic crops and strategic materials in national defense, medicine, and industry. Mechanized harvesting of cotton has been an effective way to promote the development of the cotton industry in China. Among them, a large cotton harvesting equipment, a cotton picker has been widely used in Xinjiang in western China, due to the fast, convenient, and low labor intensity. The spindle is the commonly-used core component in the cotton picker. The product quality and wear resistance of the spindle can determine the operation efficiency, quality, and economy of the cotton picker. The wear failure of the spindle is mainly manifested in the serious wear to the hook teeth. The hook teeth are the key structure of the spindle hooking and winding the cotton. Moreover, the hook teeth are in contact with the cotton plant, the bell shell, the sand, and hard particles during the operation of the cotton picker, leading to damage and peeling from the hook tooth coating. The failure of spindle hook teeth can be caused to couple with the complex and changeable field operating environment. The rear tooth tip and the tooth edge of the hook tooth were concentrated in the process of cotton picking or removal, due to the stresses of the front tooth tip. The wear in the hook tooth can often start from these parts, leading to the low wear resistance of the hook tooth. The electrolytic method can be used to passivate the front tooth tip, the rear tooth tip, and the tooth edge of the spindle hook teeth before the electroplating of the spindle, in order to improve the wear resistance of the spindle hook teeth, particularly for the service life and the collection rate of the spindle during harvesting. This study aims to explore the wear resistance of the passivated spindle and the cotton collection rate under field conditions. The unpassivated spindle and the passivated spindle were installed on different picking heads of the cotton picker. Once the working area of the cotton picker reached 0, 150, 300, 450, and 600 hm2, two kinds of spindle samples were obtained and cut for sample preparation. The wear morphology of the hook teeth was analyzed to extract the wear area of the hook teeth and the thickness of the coating. The collection rate of the two kinds of spindles was measured after harvesting. The results show that the front tooth tip of the unpassivated spindle hook tooth was easy to break, whereas, the peeling of the passivation spindle hook tooth coating was later than that of the unpassivated spindle. There was a smaller wear area of the passivated spindle hook teeth, and the coating thickness was higher at the test position under the working areas. When the working area reached 600 hm2, the wear area of the unpassivated spindle No.1 hook tooth reached 9×105 μm2, which was about 2.3 times of the passivated spindle No.1 hook tooth. There was the peeled-off coating of unpassivated hook teeth No.1 and No.2, as well as the passivated hook teeth No.1 at the test position. The passivated spindle performed better wear resistance, in terms of the wear morphology, wear area, and coating thickness. Furthermore, the collection rate of the passivated spindle was 0.2 percentage points lower than that of the unpassivated one. When the working area reached about 200 hm2, there was little difference between the collection rate two kinds of spindles. Once the working area exceeded 200 hm2, the collection rate of the passivated spindle was greater than that of the unpassivated spindle. When the working area reached 450 hm2, the collection rate of unpassivated and passivated spindles reached the maximum, which was about 96.4 % and 96.7 %, respectively. When the working area reached 600 hm2, the average wear area of the unpassivated spindle hook tooth reaches 2.9×105 μm2, which was about 2.6 times of the passivated spindle hook tooth, and the collection rate of the passivated spindle was 0.5 percentage points higher than that of the unpassivated spindle, indicating the better picking performance of passivated spindle. The finding can provide great significance for the structural optimization and modification of the hook teeth of the cotton picker.