The chemical composition, grain size and phase composition of fine particle tailing from Miyun district in Beijing were investigated by using a variety of analysis methods. Especially the phase change and its mechanism in sintering process were focused. The results show that tailing from Miyun includes 60%(by mass) SiO2 and clay mineral which decomposed at the range of 500℃ to 700℃. Orthoclase, microcline and hematite generates at about 900℃. However, the fact that orthoclase and microcline forms an eutectic compound with quartz, aluminosilicate above 963℃ means that the sample enters into the process of sintering. Augite, diopside and anorthite generates at the range of 1000℃ to 1120℃ and their content increases with increasing temperature, accompanied by increase of hematite phase and decrease of quartz phase. With sintering temperature increasing, samples colour deepens gradually, while sintering shrinkage rate, mass loss, density and Vickers hardness increase obviously at the same time. The tailings are suitable for use as raw materials for building thermal insulation materials.