In order to lower power consumption, speed up the axial conveying of materials in threshing cylinder and improve the efficiency of machine cleaning of wheat breeding plot seed combine harvester, a longitudinal axial conical cylinder threshing unit with conical short-rasp-bar tooth structure was designed. The experimental results showed that the new device could speed up the conveying of materials in threshing cylinder and lower power consumption while threshing wheat, and the amount of wheat seed residued in the shell internal was little and there was no need to do manual clearing. The threshing unit can be applied to half-feeding breeding plot wheat seed combine harvester with cyclone air cleaning devices. 