The role of calcium oxide on ash fusion properties was investigated in this work by molecular dynamics simulations and thermodynamics calculations. The variation of volume was used to identify the melting points, which was compared with the liquidus temperature calculated by the FactSage codes. The phase diagram was calculated to explain the variation of melting points with the content of calcium oxide. The radial distribution functions and species of oxygen bonding were employed to characterize the structural evolution with the different fraction of calcium oxide. The melting point of anorthite is lower than that of mullite due to less tricluster oxygen atoms. The content of CaO with high flux efficiency in (SiO2)(2)-Al2O3-CaO is found from 5.00% to 15.00%. The current modelling work on melting behaviors of minerals containing various amount of CaO may provide new insight into the mechanism of ash fusion influenced by flux.