Abstract: By using scanning electron microscope (SEM), energy dispersive Xray analysis (EDX) and Xray powder diffraction analysis (XRD), the microstructure, elemental and mineral components of interior parts of sintering deposit from the superheater surface of a fieldscale circulated fluidized bed(CFB) municipal solid waste(MSW) incinerator were studied. The results show that the deposit is rich in calcium and sulfur. The main mineral in the deposit is CaSO4. The structure of sintering deposit can be divided into root and growth part. Calcium and chlorine are higher in root than in growth part, while silicon and aluminium are much lower in the root. More alkali metals such as sodium and potassium are found in the inner layer of the root than in outer layers. Moreover, large amount of carbons present in the inner layer. The framework is more compact in root than in growth part. Vapor phase condensation and thermophoresis of submicrogranule are the leading mechanisms of the formation of inner layer of root. Transition layer and growth part are formed mainly by inertial impact of fly ashes and gassolid chemical reactions as well as high temperature sintering. The coeffect of fusion phase and chemical reactions is the primary growth motivity of the sintering deposit.