Abstract: Mineral conversion in heating process was studied by low temperature ashing, high temperature ashing and XRD. The results show that the original minerals in Zhundong coal mainly include calcite and kaolinite. With the increase of combustion temperature, they transform into fusible minerals such as fayalite and calcium. In addition, refractory minerals, ettringite and grossular, generated in ash samples, result in higher ash melting points with the decrease in SiO₂/Al₂O₃ ratio which was adjusted by adding kaolinite and alumina into the raw coal.