Abstract: A method of quenching and atomizing the melting slag simultaneously under a high pressure water jet was put forward. Experiments about cooling and pulverizing the melting steel slag and the melting blast furnace (BF) slag by a high pressure water jet of 8 to 10 MPa were conducted on a self-made slag melting and high pressure water cooling system. The results show that the atomized steel slag can be pulverized with an average particle size of 94.3μm and a composition of glass phase and Ca₂SiO₄, its reactivity is increased and the compressive strength of its cement samples aged for 28 d is 33.96 MPa, which is 8 MPa higher than that of cement samples from raw steel slag. The quenched BF slag forms flocculent structure, with degraded reactivity. The proposed method is more suitable for steel slag tapping processes than BF slag tapping processes.