In silage harvesting process, the clearance between moving and fixed blades has an important influence on the shearing performance of silage harvester cutting device, which directly affects the quality of silage cutting. Although the development of domestic silage harvester markets increases mature, the key technology of clearance automatic adjusting is still lacking for silage harvester. At present, the manual regulation is still relied on, and the complicated regulating process seriously increases labor intensity, and even delays the farming time. In order to improve the mechanization and automation level of clearance adjusting for silage harvester, an electric drive rocker arm eccentric clearance automatic adjustment device was designed. One end of the rocker arm was driven by the motor to rotate with the thread shaft, and the other end was connected with the fixed blade seat. The fixed blade rotated around the rotating shaft under the drive of the rocker arm, so as to realize the adjustment of the appropriate gap. A clearance control system based on vibration acceleration sensor was developed, and the contact state was judged by vibration acceleration signal when the fixed blade and moving blade contacted. For checking the rationality of the clearance automatic adjustment device structure and the accuracy of the control system, indoor tests were carried out at three clearance measured values of 0.2mm, 0.6mm and 1.0mm, and three chopping cylinder rotating speeds of 500r/min, 800r/min and 1100r/min. Test results showed that the clearance measured value and chopping cylinder rotating speed had a very significant effect on the clearance uniformity between the moving blade and fixed blade by the analysis of variance. With the increase of rotating speed of chopping cylinder, the variation coefficient of the clearance uniformity between the moving blade and fixed blade was increased. With the increase of clearance measured value, the variation coefficient of the clearance uniformity was decreased. The precision of left and right clearance synchronization adjusting was high, while the highest error was only 0.12%(＜1%).When the rotating speed of chopping cylinder was 500r/min, and the clearance measured value was 0.2mm, 0.6mm and 1.0mm, respectively, the variation coefficient of the clearance uniformity between the moving blade and fixed blade was 6.03%, 5.78% and 5.36%, respectively. The device and its control system realized precise clearance regulation and control, which provided technical support for the intelligent control of domestic silage harvesting device.