The effects of bean straw (BS) on ash fusion behaviors of coals (Jiaozuo (JZ) and Zaozhuang (ZZ)) with high ash fusion temperature (AFT) and the regulating mechanism were investigated from the perspectives of ash chemical composition and mineralogical property. The results showed that the AFT of JZ ash mixture decreased as the BS ash mass ratio increased, while the AFT of the ZZ ash mixture decreased rapidly (0-12%) and then increased slowly (>12%). The existence form of Al2O3, and SiO2 was converted from high-melting-point (high-MP) mullite into low-melting-point (low-MP) aluminosilicates and their eutectics with BS ash addition, leading to a decrease in AFT. With increasing BS ash ratio, the major mineral reducing the AFT was changed from feldspar into leucite. Magnesia spinel had a weaker effect on improving the AFT than that of mullite or quartz, because of their different molecular structures. The experimental ash samples were divided into three categories, based on the total contents of SiO2 and Al2O3 (A): I, A >= 78.6%; II, 72.2% <= A< 78.6%; and III, 62.7% <= A < 72.2%. As the A content decreased, the existing form of Na2O and K2O was transformed from feldspar into leucite and nepheline; the CaO, together with some FeO and MgO, was transformed from anorthite or cordierite into the more easily fusible melilite and clinopyroxene.