The heavy metal speciation distribution and leaching toxicity are analyzed in bottom ashes produced by co-combustion of sewage sludge and coal with different ratios.The results show that the biologically invalid portions,namely sulfuric,organic and residual forms of heavy metal increase to maximum with the ratio of sewage sludge to coal being 30%.Meanwhile,the leaching toxicity of heavy metal is least with the ratio of sewage sludge to coal being 30%.The conclusion of optimum ratio of sewage sludge to coal under our experiment condition is 30%,or in other words,the 30% of sewage sludge to coal ratio in co-combustion can dispose of the sewage sludge effectively as well as discharge least heavy metal toxicity to the environment.