Ao mine and sinters were observed by optical microscopy.The results showed that the structure of Ao mine is loose,The primary compositions are hematite and limonite,existing as the xenomorphic granular state.While the Ao mine content of sinter increased from 10% to 50%,the content of calcium ferrite increased,the content of magnetite,dicalcium silicate and glassiness decreased, the sintering microstructure changed from porphyritic structure to intertwining melting structure.The microstucture lead to the increasing of sinter intensity.