The invention discloses a dynamic-proportion pesticide mixing device for a pesticide spraying system of a plant protection machine. According to the dynamic-proportion pesticide mixing device for the pesticide spraying system of the plant protection machine, using and operating intensity is reduced, pesticides can be mixed more uniformly and thoroughly, injuries to health of the human body are reduced, and environmental protection is achieved. An outlet end of a proportional pesticide mixing water inlet branch pipe is provided with a proportional pesticide mixing pump, a water turbine is arranged at the bottom of a primary mixing box, an output shaft of the water turbine perpendicularly stretches into the primary mixing box, a stirrer is arranged on the output shaft of the water turbine, a spraying device is arranged on the upper portion of the primary mixing box by surrounding the inner wall of the primary mixing box, a sprayer of a washing bottle perpendicularly goes deep into the primary mixing box, a lower suction opening of the proportional pesticide mixing pump is provided with a flow regulator, the exterior of the flow regulator is connected with a liquid suction pipe, the lower end of the liquid suction pipe is inserted to the internal bottom of the primary mixing box, and the exterior of an outlet of the proportional pesticide mixing pump is connected with a pesticide liquid outlet pipe. The dynamic-proportion pesticide mixing device is installed on the mechanical plant protection pesticide spraying system and used for uniformly mixing the pesticides according to the dynamic proportion.