Coal-ash　fusibility　exhibits　corresponding　relations　to　its　chemical　composition　and　mineral　composition,　in　which　acidic　oxides　can　increase　the　ash　fusion　temperature,　but　the　basic　oxides　play　a　role　in　helping　fusion　and　can　reduce　the　ash　fusion　point.　Since　the　ash　fusion　temperature　always　depends　on　the　final　multi-phase　equilibrium　of　coal-ash　composed　of　various　element　compositions,　the　ternary　phase　equilibrium　diagram　could　often　be　used　to　predict　and　explain　the　variations　of　ash　fusion　temperature.　The　above　important　results　show　not　only　adding　different　additives　into　the　coal-ash　changes　its　ash　fusibility,　which　has　been　effectively　applied　to　select　a　suitable　way　in　discharging　ash-slag　and　for　coal　gasification　process,　but　also　adding　appropriate　additives　into　the　alkaline　coal-ash,　yielded　from　coal　catalytic　gasification,　forms　a　stable　silicate　compound,　which　resulted　from　the　interaction　among　the　vitreous　lattice　oxides　(e.　g.　SiO2),　the　modified　median　lattice　oxides　(Al2O3,　Fe2O3,　etc.)　and　modified　meshwork　oxides　(Na2O,　CaO,　MgO,　etc.)　under　a　certain　calcinations　temperature,　which　has　been　successfully　adopted　for　the　harmless　treatment　for　the　alkaline　coal-ash.