The Shell coal gasification craft is the advanced second-generation coal gasification craft, which combines with melting slag and pressurize air platform. The characteristics of coal which are coal ash ,slagging resistance, ash fusion and so on plays important roles in ensuring the stable operation of the device.It’s very important to change the melting characteristics of coal by means of adding accelerant for the more ash and high melting point coal in order that the gas furnace can slag smoothly.The influences of the limestone used as cheap accelerant on the Shell craft were discussed.The results showed that the ash fusibility temperature of coal,the viscosity of the coal ash and the slagging of coal was reduced after adding limestone,so as to ensure the stable operation of the device.