In order to improve the strength of iron ore pellets containing carbon（IOPC), proposed a new double layer structure which wraps a iron ore layer outside the IOPC. The strength and metallization rate of different thickness outer layer were tested. And the formation mechanism of strength was analyzed. The results show that the strength of moderate outer layer of composite carbon- containing pellets can be improved effectively. The drop strength of this new pellet is 2 times larger than that of ordinary IOPC. The compressive strength with 400℃ preheat is 147. 6 N per pellet. The compressive strength decreases with increasing temperature while the temperature is above 900℃. After 1150℃ constant temperature reduction for 30min, the compressive strength can reach 2080 N. And it was found that the new pellet can effectively improve the utilization rate of C, the metallization rate of pellet (nC/nO=2∶3) after reduction is 93. 90%, and the metallization rate of outer layer is 92. 46%. By microstructure analysis, it was found that the outer layer of pellets generated dense metallic iron shell after reduction. This special mechanical property of the shell is the main reason for the increased strength.