The invention discloses an automatic corn threshing device, which comprises a cylindrical kernel storage drum. The lower end of the kernel storage drum is provided with a discharging hole, the inner bottom surface of the kernel storage drum is provided with an annular sleeve communicated with the discharging hole, a conical guide barrel is formed at the upper end of the annular sleeve, and the upper end of the guide barrel is provided with a plurality of threshing teeth. A cover plate is fixed to the top end of the guide barrel, the center of the cover plate is provided with an open slot penetrating the front end face of the cover plate, the front end of the kernel storage drum is provided with a feeding groove communicated with the open slot, a pressing mechanism is arranged on the coverplate, and a feeding mechanism is inserted in the feeding groove of the kernel storage drum. Manual operation is substituted by automatic equipment to realize fresh corn threshing, so that operating efficiency is effectively improved, and labor intensity of operating personnel is relieved.