Abstract: KH₂PO₄—cement is used to soildify/stabilize the Pb contaminated soil. Leaching tests are conducted to study the leaching characteristics and mechanism of Pb in solidified bodies under acid rain soaking, and the effects of KH₂PO₄ addition, leaching time and leachate pH are took into account. The results show that KH₂PO₄ is effective to stabilize the Pb-contaminated soil. The Pb leaching is related to pH of leachant directly, and the leaching amount of Pb increases with acidity. What’s more, Pb leaching is also related to pH of leachate, and strong alkaline of leachate is conducive to the Pb mobility. For the acid solutions with pH of 2 and 5, the cumulative leaching ratio of Pb changes with time linearly, but the two-stage linear variation is founded for the acid solutions with pH of 3. pH of the leachate is in relation to the leaching amount of alkaline materials in S/S bodies. The controlling leaching mechanism of Pb changes with leachant pH, and it is presented that the leaching mechanism changes from dissolution to diffusion with the increasing leachant pH.