Abstract: Aiming at the present situation of air separation units in a steel plant, a rational method of calculating the costs of oxygen, nitrogen and argon was proposed by considering the air separation process and the energy consumption of air-separation products, and was used to calculate the energy consumption and the apportioning proportion of air-separation products. The presented method can not only solve the problem that the energy consumption of single product cannot be accurately calculated because oxygen, nitrogen and argon are by-products one another, but also eliminate the disadvantage that the apportioning proportion is arbitrarily controlled.