Phosphoric acid and steel slag were used to prepare modified steel slag, then, environmentally friendly styrene butadiene rubber were prepared by synthesizing styrene butadiene and carbon black partially substituted by modified steel slag. The effects of ratios of phosphoric acid/steel slag, modified steel slag/carbon black and accelerator/sulfur on the mechanical properties of prepared samples were studied, respectively. The results showed that when the mass ratio of phosphoric acid/steel slag was 10:250, modified steel slag showed the optimal pore structure, the specific surface area, pore volume and average pore diameter were 15.093 m2/g, 0.0868 mL/g and 24.87 nm accordingly. With the mass ratios of modified steel slag/carbon black and accelerator/sulfur as 260:250 and 10:15, the prepared sample presents the best comprehensive performance in terms of mechanics and economy, tensile strength 23.7 MPa, Shore A hardness 67.9 and tear strength 41.2 kN/m.