China's electric arc furnace (EAF) slag reserves are huge, the problems of EAF slag resource application need to be solved urgently. In this study, high temperature holding and slow cooling treatment were used to treat the slag. The phase and structure of the slag were analysed by means of X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. To analyse the migration pattern of iron elements and to study the interaction between EAF slag basicity and magnetic separation efficiency. The results show that, there is an obvious layering phenomenon during the cooling slag, and the top layer is the Fe-rich layer. The slow cooling treatment makes the Fe-rich phase grow sufficiently and improves the dissociation efficiency of the Fe-rich phase in the crushing process. As the basicity increases, the thickness of the iron-rich layer gradually decreases and the iron element is transferred to the RO phase, while the concentrate yield decreases. Multi-stage wet weak magnetic separation of treatment slag resulted in the highest concentrate yield of 49.05 % at an basicity of 1, with a T.Fe content of 56.711 %, and 70.32 % of the iron component entering the concentrate. The concentrate can be returned to the steelmaking process instead of the charge, and the tailings can be used to make high value-added products.