Abstract:The characteristics of iron reduction and growth of metallic phase in deep reduction of a nickel smelting slag by carbon were discussed in the paper. The effects of the reduction temperature and time and the additive of calcium oxide on the generation and growth were investigated in detail．The results showed that raising the reduction temperature and the reduction time and adding a certain amount of calcium oxide was beneficial to the generation and growth．In the reaction process, the small droplets of metallic iron which were reduced gathered towards the larger drops and existed in the form of solid iron particles in the reduction of the material after cooling by water. The metallic phase of grain growth could be divided into three stages, reduction to iron, gathered into drops and cooling to particles stage.