Aiming at solving the blocking of screw conveyor on header of rape combine harvester, an automatic clearance adjusting mechanism was designed. The maximum pretension and displacement were determined to be 366N and 50mm, respectively, through statics and kinematics analyses of the screw conveyor. Torque sensor and high-speed camera technique were used respectively to record torque on the shaft of conveyor and displacement，parameters tests of the mechanism were conducted and the results indicated when pretension was 293N and stiffness was 12.65N/mm，maximum torque of conveyor was 8.267N·m，which was decreased by 40.7%，maximum displacement of the slider was 10.2mm， and parameters of adjusting mechanism were optimal. The influence of the adjusting mechanism on performance of conveyor tests showed that adding the adaptive adjusting mechanism could obviously reduce torque and increase maximum feed quantity，when speed was in range of 150~300r/min, the feed quantity was 1.5~3.5kg/s. Torque was decreased by 23% when speed was 150r/min，feed quantity was increased by 0.5kg/s in experimental group，which was increased by 17.8%. When feed quantity was fluctuated from 1.0kg/s to 3.0kg/s and 1.0kg/s and from 3kg/s to 1.0kg/s and 3.0kg/s， maximum torque was decreased compared with steady feeding quantity of 3kg/s. Field experiment showed that the clearance adaptive adjusting mechanism could adjust the clearance between screw conveyor and bottom plate in time according to the change of feed quantity during harvesting operation，therefore，it could improve the adaptability of header to fluctuation of feed quantity and relieve blocking.