Abstract: Abstract: Vigorously developing precision and advanced agricultural equipment is one of the ten major areas emphasized in the “Made in China 2025” blueprint, the core strategy of agricultural mechanization centered on improvement of the performance of key mechanical components. With the increase of cotton planting area, the application of modern mechanized cotton pickers becomes more and more attractive, especially in Xinjiang, China, where the mechanization degree in harvesting is relatively higher than the other regions in China. Cotton picker is agricultural machinery of mechanization of cotton harvesting, and spindles in cotton picking machinery are the key component. As the work condition of cotton picker spindle is complex and changeable during the picking process, the contacting interfaces of spindle with cotton fiber involve gradually in the aspects of the stress state, topography, and surface microstructure etc. Surface coating wear of spindle are common with the increase of picking time, leading to the degradation of the spindle and drop of harvesting rate. Accordingly, a lot of effort has been made on improving its wear resistance in the past decades due to the problem of inadequate lifetime of the spindles. However, the previous researches are lack of investigation on failure process of the spindle, especially the mechanical analysis on the spindle surface. The main objective of this study was to reveal the wear process of spindle by analyzing the wear topography of spindle in the cotton picking process. Furthermore, based on the numerical method of finite element analysis, the mechanical performance of spindle was investigated for normal operating parameters of the spindle in field work. Therefore, the solid model of cotton picker spindle in the picking process was established by SolidWorks software along with ANSYS software. The stress and strain distribution of the spindle in the removal cotton process were simulated by the finite element analysis. The numerical simulations results showed that the surface of spindle’s teeth sustained more severe stress than the other portions. In terms of a single spindle’s tooth, the larger diameter edge of spindle’s teeth bore a greater contact stress than smaller diameter edge, leading to the beginning of wearing in the surface coating along the larger diameter edge of spindle’s teeth. In cotton picking process, the spindle is rotated at high speed, at the same time, the spindle rotates with roller while rotating itself. Under the combined actions of tangential friction forces and axial friction forces on the rotating spindle surface, the resultant force direction of the friction force had a certain inclination angle to the axis of spindle, and the inclination angle changed in real time. The surface coating of spindle’s teeth was worn gradually and the characteristic “broom type” wear scar was formed as the picking time increased. Moreover, the fracture of spindle was due to torsion formation, and dangerous section occurred between 8th and 11th teeth from the root of spindle. When the spindle was installed correctly and the lubrication was adequate in the cotton picking process, the wear of the spindle’s bevel gear was caused by the plastic deformation. It was mainly because of spindle deformation was concentrated on the bevel gear when the external load increased instantaneously, such as branches, debris, and gravel was suddenly brought into picking room in cotton picking process. These numerical simulations results were consistent with the microstructure and morphological characteristics of the worn spindle’s surface with electroplated chromium coatings by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS). The research results will helpful for reducing failure of spindle (fracture and wear), which makes it possible to prolong the service life of spindle used, and has remarkable economic benefits and important social significance.