In order to lower the operation cost, the series of rotary kiln mix block with powder in calcining. The green ore measured by the electronic belt scale, belt conveyor, steady bunker, and air lock valves in the reservoir will be fed into rotary kiln end directly. The steady bunker is located only in kiln end in order to lower the cost. Ore put into the rotary kiln will be heated first. Ore in the kiln moves oppositely to the hot air. Ore is heated to the reduction temperature in the heating area and then enters into the reduction area where the temperature of the central flame zone is kept at about 1000 degree celsius and the temperature of the steam zone is kept at about 700 degree celsius. Then the ore is reacted with the reduction gas and become magnetic ore for dressing by magnetic separation.