Abstract: With rapid development of livestock husbandry, fresh straw is urgently needed as feed for livestock．Corn straw harvesting can not only solve source of livestock feed, but also increase farmers' income．During operation of forage harvester, moving blades used for cutting feed will wear out．After wear out, situation of continuous cutting will occur, so harvester needs to be stopped and sharded．After sharpening, blade is short, and clearance between static blade and moving blade becomes larger, which directly affects quality and efficiency of feed cutting．In order to solve this problem, an automatic adjustment device for blades clearance of forage harvester was designed．It could start with one key, automatically adjust clearance, effectively reduce labor intensity, and ensure consistency of clearance between left and right sides of blades．The automatic adjustment system has advantages of convenient operation and high intelligence, saving farming time and improving quality of feed cutting and working efficiency．