Abstract: Cotton is an important strategic material. With the increase of cotton planting costs, improving the level of mechanized harvesting has become an important way to improve the economic benefits of cotton planting. The main cotton harvesting machinery used in China is the horizontal spindle type cotton picker. In the process of production practice, the domestic cotton pickers have problems during high-speed operation, such as improper matching of picking speed ratio coefficient, badly gear worn and poor reliability of picking head transmission system. In view of the above problems, this paper optimized the transmission system of picking head based on the comprehensively consideration of the operating speed, transmission system reliability, operation quality and other factors, aiming to increase the operating speed of the cotton picker, improve the reliability of the picking head transmission system and the operation quality of picking head. According to the structure and working principle of the horizontal spindle type cotton picking head, the transmission route and transmission ratio of picking head transmission system of cotton picker were analyzed and calculated firstly. Then, the picking mechanism and picking conditions, such as the range of picking speed ratio coefficient of cotton picker, the actual number of turns needed to pick cotton petals and the picking time of spindle, were determined through virtual simulation technology and theoretical analysis and calculation. Meanwhile, the roller power gear in the transmission system of the picking head was selected as the optimization object, the tooth number of roller power gear, modification coefficient of the upper gear on clutch, modification coefficient of roller power gear and addendum height coefficient were selected as design variables, and the objective function and constraint conditions were established. The Genetic algorithm and 1stOpt software were used to optimize the transmission system of picking head. The optimization results were as follows: the number of teeth for the roller power gear was 72, the modification coefficient of the upper gear on the clutch was -0.14, the gear modification coefficient for the roller was 1.208, and the addendum height coefficient was 1.25. A cotton picking performance test bench was built combining the operation requirements of the cotton picker. The operation performance of picking head before and after optimization was verified on the test bench with the factors as follows: picking roller speed was 113-143 r/min, the operation speed was 5.93-7.20 km/h. The results showed that the working speed of the picking head was increased from 6.4 to 7.2 km/h, increased by 3.6%, and the work efficiency increased from 4.86 to 5.47 hm2/h, increased by 12.5%. Under the working speed of 7.2 km/h, compared with before optimization, the collection rate increased from 90.4% to 93.7%, increased by 3.6%, and the impurity rate decreased from 10.28% to 9.72% and decreased by 5.4%, which verified the rationality of the optimization of the picking head transmission system in this paper. The study can provide a reference for the development of picking head of cotton picker.