Spindles in cotton picking machinery are the key component, wear of the spindles significantly reduces harvest efficiency of the cotton picking process. To improve its wear resistance, the substrate surfaces of spindles are usually electroplated with chromium coating. But the failure process and wear mechanism of the spindle have not been studied so far. In this paper, based on the surface analyses and wear behavior of spindles of a cotton picker in field work, the test results showed that the worn surface was smoother and wear trend of surface topographies tend to consistent along with the rotation direction of the spindle and found a significant reduction in roughness and coating thickness. The coating of the spindle surface has not been damaged in the picking process, the wear mechanism was mainly abrasive wear. After the worn out of surface coating, abrasive wear is always present accompanied by oxidation wear. Multi-oxides were deposited on the substrate surface; the oxide particle was sheared by cotton fiber in the subsequent picking, leading to an increase in surface roughness and aggravating substrate wear. These in filed wear mechanisms and processes of spindles could be of help for the design and surface modification with longer working life.