The invention relates to a two-step steel slag treatment method using oxidation desulfurization and reduction dephosphorization, and belongs to the technical field of iron and steel metallurgy and resource utilization. According to the steel slag treatment method, the problem of S and P enrichment in the prior art of steel slag recycling is solved. The two-step steel slag treatment method using oxidation desulfurization and reduction dephosphorization comprises the following steps of 1, carrying out oxidation desulfurization of steel slags, specifically, a mixture of Ar and O2 is introduced into the molten steel slag, oxidized SO2 is removed from slag phase, and the removal rate of the S is 82%-97%; and 2, carrying out gas-based reduction dephosphorization of the desulfurized steel slag obtained in step 1, specifically, the reducing gas is a mixture of CO and CO2, the removal rate of the P is up to 80% or above, and reduced P2 is removed from the slag. According to the two-step steel slag treatment method using oxidation desulfurization and reduction dephosphorization, the problem of removing the S and the P from the steel slag is thoroughly solved, the recycling utilization ratioof the steel slag is greatly improved, and the full utilization of the steel slag, the S and the P is achieved, so that the cost of steel-making is reduced, the utilization values of the S and the P are improved, and the two-step steel slag treatment method has a broad application prospect.