The invention discloses an artificial steel slag aggregate and a preparation method and application thereof. The preparation method comprises the following steps: step 1, grinding steelmaking tailingsby using a ball mill to obtain uniform steel slag powder; 2, weighing Portland cement, an admixture fine powder and steel slag powder, and conducting uniform mixing to obtain an aggregate raw material; 3, preparing an additive aqueous solution; 4, putting the aggregate raw material into a ball forming mill, and uniformly spraying the additive aqueous solution prepared in the step 3 to form balls,so as to obtain spherical artificial steel slag aggregate; step 5, putting the pelletized aggregate into a closed environment or a natural environment for pre-curing; and step 6, putting the pre-cured aggregate into a carbonization device for carbonization treatment to finally prepare the artificial steel slag aggregate. The artificial steel slag aggregate prepared by the method can achieve the goals of safety and high strength, the crushing index of the aggregate can reach 9.26% and reach the I-grade aggregate use standard, the production process is simple, the solid waste is recycled, the carbon dioxide is absorbed and cured, and the artificial steel slag aggregate is free of burning, low-carbon and environment-friendly.