To solve problems, such as threshing cylinder blockage and the decline of operating performance caused by feeding rates fluctuation in the field, the device for adjusting concave clearance and monitoring threshing cylinder load was designed. The designed device and system consisted of concave clearance adjusting system and the oil pressure monitoring system on the rear side of the concave. The oil pressure on the rear side of the concave was used to reflect the threshing cylinder load. During the field test, the oil pressure on the rear side of concave was monitored. The STM32 microcontroller was used to collect and preserve the signal of oil pressure signal on the rear side of concave. During the field test, the relationship between the oil pressure and the feeding rates was analyzed. The influence of concave clearance on the oil pressure on the rear side of concave was analyzed in detail. The results verified that the designed concave clearance adjustment device can adjust the concave clearance rapidly and stably. The displacement sensor can display concave clearance in realtime. The adjustment range of concave clearance was 35~60mm, the speed of the hydraulic cylinder can be adjusted in the range of 0~10mm/s. The oil pressure on the rear side of the concave tended to increase with the increase of feeding rates. The function relationship between the oil pressure on the rear side of the concave and the feed rates was obtained by analyzing the obtained experimental data, and the corresponding correlation coefficient was 0.9813, which indicated that the function was consistent with the theoretical analysis. It was verified that the threshing and separating loss was increased with the increase of feeding rates. More concretely, when the feeding rate was increased from 3.4kg/s to 6.0kg/s, the oil pressure on the rear side of the concave was increased from 732N to 1114N, and the threshing and separating loss was increased from 0.54% to 1.08%. Under the rated feeding rates (6.0kg/s), when the crop was evenly fed, the hydraulic pressure of the left and right cylinders was fluctuated in the range of 450~660N, the pressure change of the left and right cylinder was consistent with each other. The oil pressure on the rear side of concave tended to decrease as the concave clearance was increased. The threshing and separating loss was increased as the increase of concave clearance. In case that the concave clearance was increased from 35mm to 45mm, the oil pressure on rear side of concave was decreased from 1114N to 758N, and the threshing and separating loss was increased from 1.08% to 1.31%. It proved that it was feasible to reduce the threshing cylinder load by increasing the concave clearance. Under the conditions that the feeding rate was 6.0kg/s and concave clearance was 35mm, the threshing and separating system had the best performance, the corresponding pressure on rear side of concave was 900～1320N. The concave clearance adjust device can achieve a fast and stable regulation which provided a scientific basis for adjusting the concave clearance automatically according to the load of threshing cylinder load.