Abstract: In order to improving corn threshing quality, The PLC electric control system was optimized by fuzzy control. Firstly, based on single longitudinal axial corn threshing device, the effects between roller shaft speed, threshing interval and speed of harvester on threshing quality were analyzed; Crushing rate model comprehensive considering barrel shaft speed, threshing spacing and harvester forward speed was achieved by triad quadratic general rotation combination experiment. The result that the effect between threshing interval on crushing rate model was not significant, barrel shaft speed and harvester forward speed were taken as control variable, and then the fuzzy PLC Control System was designed. This system was tested, the result showed that the system has a fast response speed and high reliability.