Mechanochemical method was adopted to study the stabilization of Pb in a Pb-containing smelting slag when different stabilizing agents were added. The chemical composition and leaching toxicity of slag were analyzed. The stabilization mechanism of lead in the slag was studied by simulated acid treatment. The effects of four stabilizing additives (iron powder, aluminite powder, hematite and ferrous sulfate) on the leaching toxicity and stabilization rate of lead were examined. The results showed that the promoting effect of four additives on the stabilization of lead followed the order of iron powder > aluminite powder > ferrous sulfate > hematite. The optimum conditions for the stabilization were the amount of stabilizer at 8%(w), mass ratio of grinding media to material 8:1, milling time 1.5 h and milling speed 400 r/min. Under the optimum conditions, the leaching toxicity of lead was 0.258 mg/L and the stabilization rate of lead reached 99.77%. The adsorption of lead ion by the iron oxides on the surface of milled iron particles was the main reason for the decrease of Pb leaching toxicity.