Microstructure analysis shows quartz remains more or less in used silica brick for coking chamber of coke oven, and quartz gradually becomes metastable cristobalite and then translates into tridymite in used brick for high temperature combustion chamber. Phase change of silica brick only limits to transformation of quartz and metastable cristobalite. When finished, structure of silica brick tends to stable. Carbon sedimentates and graphitizes helping to protect the silica brick and improve heat conductivity of silica brick for coking chamber.