In order to solve the problem that corn thresher can not automatically adjust the threshing clearance and reduce the mechanical damage in the process of corn threshing, the floating corn single panicle threshing device was designed. The threshing device was mainly composed of clearance adjustment device, feeding hopper, discrete roller, threshing roller, differential roller, etc. The clearance adjustment device could float and automatically adjust threshing clearance. It can adapt to the differences in the diameters of corn ears, which was conducive to reduce broken rate and increase threshing rate. When the water content of grain was below 25% and the speed of discrete roller and threshing roller was not more than 800r/min, the threshing device did not result in the fracture of corn cob. The feeding hopper realized the function of automatic separation of corn ears and discharge one by one. The optimum tilt angle of feeding hopper was 40° and the feeding height of corn ear was 132cm. Three parameters, including discrete roller speed, threshing roller speed and differential roller speed were selected as the input variables, and broken rate and un-threshing rate of corn grain were used as the test indexes. Parameter optimization experiment was completed on the floating corn single panicle threshing device by the method of quadratic regression orthogonal rotary combination. The optimization results showed that the discrete roller speed was 234r/min, the threshing roller speed was 511r/min and the differential roller speed was 91r/min. The actual grain broken rate was 0.25%, the actual un-threshing rate was 0.76% and the integrity rate of corn cob was 100% under the optimal parameter combination.