In view of the problems of traffic ability and the precise control of fertilizer application of the additional fertilizer machinery, the variable rate fertilization system of triwheel high frame operation vehicle was designed. It was composed of mechanical fertilization system, hydraulic system and electronic speed control system. Its trafficable height was 1.2m, and could apply fertilizer to four lines of corn at the same time. During operation, the hydraulic system powered hydraulic motor to drive the outer groove wheel type fertilizers. The control of fertilizer application was realized by electronic speed control system adjusting the rotational speed of fertilizer shaft, using closedloop control and the microprocessor STM32F103R8T6 core, combining the setting parameters such as dose rate and the speed signals being detected to calculate the advancing velocity of high frame operation vehicle and the theoretical rotational speed rotational and the actual rotational speed of fertilizer shaft and displaying them, adopting the incremental PID algorithm to control electrohydraulic proportional flow valve. The laboratory test showed that average coefficient of variation of the fertilizer amount was minimum when fertilizer trough work length was 30 mm. The fitting equation of fertilizing amount and rotational speed was determined. PID parameters was set as proportional coefficient of 1.2, the integral coefficient of 0.02, and the differential coefficient of 0.4. The field experiment showed that the average deviation of fertilizer application was 0.84%, the average coefficient of variation was 1.852%, realizing mechanized and precise additional fertilizer for corn.