Abstract: Two coals (Ninglu and Xiaotun) with low and close ash fusion temperature were selected and blended with Tianchi coal having a high fusion temperature. The results show that the ash fusion temperature of the blended coal with Xiaotun increases more significantly with increasing ratio of Tianchi coal; and that with Ninglu coal varies little. Mineral transformation processes of blended coal-ashes were examined by XRD. The combustion residue of Ninglu coal contains lots of minerals such as hematite and anhydrite which have negative effects on the formation of mullite. The ash fusion temperature could not increase dramatically for the lack of mullite with high fusion temperature and playing a key supporting role in coal-ash melting. Some experiments of blended coals were carried out in a drop tube furnace to simulate slagging process in power plant boilers. SEM was applied to analyze the surface morphology of different residues. It is proved that Xiaotun coal blended with Tianchi coal could remarkably improve slagging characters.