Abstract: In order to meet the need of low oxygen content under the deep desulfurization conditions of hot metal, the variation of oxygen content in hot metal was studied by the thermodynamic method when the Al-C-O equilibrium reached. Compared the deoxidation constants of the C or Al single deoxidizer with the Al-C complex deoxidizer, it is found that at 1 573 K the deoxidation ability of Al-C complex deoxidation is stronger than that of C deoxidation during hot metal pretreatment. The equilibrium curve of Al-C complex deoxidation at 1 573 K can be drawn by using the thermodynamic theory. If the temperature is constant, the deoxidation ability of Al-C complex deoxidation increases with the carbon activity a_C increasing; but if a_C is constant, the deoxidation ability of Al-C complex deoxidation lowers as the temperatures rises.