With form analysis of heavy metals, the transportation experiment and theoretical analysis of heavy metals by simulated rain and acid rain showering were carried out, the effects of sludge composting on Bioavailability of heavy metals in sludge were studied. The results indicated that the ratio of the unsteady species of heavy metals in sludge is reduced after composting. The heavy metal elements in leachate of original sludge treated with acid rain had moved down to the layer of soil with the depth of 16 cm,while the content of heavy metal of treated one is lower and only a small quantity of elements had moved down to the deep layer of the soil. Both the volume and the depth of the composted sludge are lower apparently than those before composting. The experiment and theoretical analysis verified that both the transportation of heavy metals in soil and the bioactivity of heavy metals are reduced by sludge composting.