In order to reduce the labor intensity of manual topping, the environmental pollution of chemical topping and the over-topping of the traditional “one-size-fits-all” topping mechanism, a double disc clamping topping mechanism was designed by analyzing the manual topping process. Based on machine vision, a single-line prototype of the topping device was designed to realize the automatic control of the whole process of cotton topping. It was mainly composed of topping mechanism, visual inspection mechanism, motion mechanism, cotton top recognition and control system. Based on cotton field research, structural calculation and pre-test, the overall structure and key component dimensions of the topping device were determined. Combined with the research basic and practical application of visual recognition, the YOLO v3 algorithm was selected to build the cotton top recognition and control system, realize the recognition and positioning of cotton top, and complete the motion control of the topping mechanism. Taking cotton in the topping stage as the research object, the cotton top recognition test, the topping mechanism performance test and the field comprehensive test were carried out. The results showed that the average recognition rate of cotton top recognition test was 93%;the average topping rate of the performance test of the topping mechanism was 94.67%;the average recognition rate and average topping rate in the field test was 85.33%, and the average topping rate was 78.22%. The research result can provide reference for the precise and intelligent research of cotton topping.