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In order to meet the requirements of maize combine harvester for threshing device, the breakage rate and the non threshing rate of maize should be reduced in the threshing process of ear with high moisture content. The threshing nail teeth with composite structure of rubber and carbon steel layers were improved and designed. Besides NBR, NR and EPDM were self-made as the materials of outer structure of composite nail teeth. The effects of composite nail teeth in different outer materials on threshing performance of maize ears (the breakage rate and the non threshing rate of maize) and self anti-fraying performance (loss weight on damage and abrasion of surface tissue) were studied by bench tests. The results of threshing tests showed that when the moisture content of maize grain was 29.7%~30.5%, and the feed quantity of maize ear was 8~12kg/s, the breakage rates of maizes in NBR, NR, EPDM composite nail teeth and traditional carbon steel nail teeth were 4.85% to 7.27%, 3.77% to 6.23%, 2.92% to 4.88% and 6.90% to 10.35%, respectively, and the non threshing rates of maize were 0.41% to 0.82%, 0.35% to 0.78%, 0.30% to 0.69% and 0.24% to 0.59%, respectively. The results of abrasion tests showed that from the macroscopic abrasion of the surface, the gullies of the NBR layer were obvious and the abrasion of surface was serious, the number of pits in the EPDM layer was far less than that of the NR layer, neither of which led to the failure;from the microscopic morphology of the surface based on SEM, the number of cracks in the NBR layer was the most and the structure was discontinuous, and the holes in the NR layer weakened the combination between the tissues. Most of the structures of EPDM were relatively complete and continuous and had strong resistance to external forces. The comprehensive results showed that under the high moisture content of maize grain, rubber composite nail teeth could significantly improve the threshing performance of ear, among which EPDM composite nail teeth had the best comprehensive effects in threshing and self anti-fraying performance, the breakage rate of maize was 52.85%~57.68% lower than that of traditional carbon steel nail teeth, and the non threshing rate of maize was similar to that of traditional carbon steel nail teeth, meeting the requirements of technical specifications for threshing quality evaluation of maize harvester.