Abstract: The coal ash fusion characteristics of high fusibility coal blending with two low fusibility coals respectively were studied. The data were analyzed using quantum chemistry methods and experiment from micro- and macro-molecular structures. The results show that Ca²⁺, as the electron acceptor, easily enters into the lattice of mullite, causing a transition from mullite to anorthite. Mullite is much more stable than anorthite. Ca²⁺ of anorthite occupies the larger cavities with the [SiO₄]^4- tetrahedral or [AlO₄]^5- tetrahedral rings respectively. Ca atom linked O weakens Si—O bond, leading ash fusion point to reduce effectively. The chemistry, reactivity sites and bond-formation characteristics of minerals can well explain the reaction mechanism refractory minerals and flux ash melting process at high temperature. The results of experiment are agreed with the theory analysis by using ternary phase diagrams and quantitative calculation.