Fines generation of lump coal is a most important limiting factor for efficient production in the COREX process. In this paper, the fines generation of lump coal has been examined based on simulation experiments of the relationships of coal char conversion with temperature and heat absorption. According to the results, in the early stage of coke formation in the melter gasifier, lump coal absorbs large amounts of heat but without significant increase in its high temperature strength. Strength was only improved at later stages of the coke forming process. Residual coal was also found in most tuyere coke samples illustrating that the lump coals added to the melter gasifier were not completely transformed into coke when they arrived at tuyere region. An improvement in the high temperature performance of lump coal is speculated be limited in the melting gasifier due to the low coke forming rate which could become the core factor of fines generation of lump coal in the melting gasifier. Thus, we suggest preheating the lump coal before it is added to the melting gasifier as a solution.