The study provides a novel way for the utilization of coal fly ash, and enriches the sintering mechanism in preparation of low-cost, high performance mullite based ceramic. The phase evolution, microstructure, densification behavior and flexural strength as a function of the sintering temperatures, were investigated by XRD, SEM and evaluated by density, open porosity and shrinkage and three point bending method, respectively. Secondary mullite nucleates from the dissolution of alumina in transient liquid phase at 1300°C. Above 1400°C, mullite content increases and the densification is promoted with increasing temperature. Fast densification takes place and high flexural strength of 149MPa is achieved at 1600°C.