In order to solve the problems of low utilization rate of straw round baler microbial inoculum and uneven spraying of microbial inoculum, a straw round baler microbial inoculum spraying control system based on feed quantity feedback was designed. According to the working principle and control characteristics of the self-propelled round baler, the design of the microbial inoculum spraying device, the design and selection of key components, the software design and the construction of the control system were carried out. In order to obtain the relevant parameters of the control system and test the effectiveness and stability of the control system, bench test and field tests were conducted. The relationship between PWM duty cycle and dynamic flow rate of nozzle spraying was obtained in the bench test, which provides the basis for intelligent control of microbial inoculum spraying. The field test showed that the total microbial inoculum spraying volume and auxiliary circuit microbial inoculum spraying volume were changed accordingly with the change of feed quantity. This control system can meet the design requirements, and can be adjusted according to the change of feed quantity, which can effectively improve the utilization rate of microbial inoculum.