To improve straw production efficiency and solve problems of straw discharge low uniformity and unadjustable feeding speed in traditional average feeders, an automatic variable speed straw average feeder based on principle of reverse differential motion and PLC control was designed．It comprised a frame, electric frame, drive shaft, driven shaft, box welding, grass roller, scraper side plate, motor, scraper, and PLC control system．PLC control system collected output straw layer thickness information of average feeder and motor current information of next step．After PLC program was calculated, information was transmitted to inverter to adjust motor speed．Calculation of differential motion speed determined whether met work demand and used Solidworks simulation static stress to analyze grass roller mechanical properties, calculated the number of blocks, and selected suitable arrangement mode．Whole-machine test showed that equipment could automatically adjust average feeding speed according to requirements, with a standard deviation of 3.26 mm for straw layer thickness, and average feeding efficiency of 3423 kg/h, which could meet work requirements．