The variation of heavy metal speciation during the bioleaching of sludge were carried out. By virtue of heavy metal speciation transformation pattern, the transformation mechanism of heavy metal speciation during the bioleaching could be judged indirectly. The test results show that the bioleaching process of Cu, Ni, Cd are mainly dominated by direct mechanism, the bioleaching process of Zn is mainly dominated by indirect mechanism, and bioleaching process of Cr, Pb are mainly dominated by combined mechanism, while the chemical principle between Cr and Pb are different.