Abstract: The effects of paper mill residues (delinking sludge, paper mill sludge, municipal sewage sludge) addition on slagging tendency of wheat straw were investigated using ash melting point test system, X-ray fluorescence (XRF) and powder X-ray diffraction (XRD). The differences between other 4 common additives were also discussed. The results show that addition of delinking sludge and paper mill sludge behaves better than municipal sewage sludge in blending range of 3% to 10%, while softening temperature of wheat ash tends to get the highest value when adding 5% paper mill sludge. Along with the blends increasing, Al₂O₃ plays an important framework structure modification role while adding paper mill sludge. While generation of feldspar such as orthoclase and anorthite takes place, the softening temperature decreases. In addition, silicon aluminum garnet is more likely to form to enhance the fusion characteristic temperate while adding delinking sludge. On the contrary, formation of high melting point material(CaSiO₃)inhibits low melting silicate by adding paper mill sludge. Components analyses indicate that crystal structure of SiO₂ is changed along with municipal sludge added. Sludge used as anti-slagging additives is promising.