<p>High-alumina coals (HACs) cannot be directly used as feedstock for slag-tapping entrained-flow gasifiers owing to their high ash fusion temperatures (AFTs). Coal blending may offer a practical method for regulating ash fusibility. However, the regulatory mechanisms for HACs remain unclear. This study investigated AFT reduction in HACs through coal blending, employing a high-temperature stage microscope for in situ observation of ash melting processes and interactions between HAC ash and blended coal ash. The ash fusion mechanisms were clarified through analysis of mineral transformation and aluminosilicate structure variations. Results indicated that coal blending effectively lowers the HAC AFTs by converting high-melting-point miners such as Al₂O₃ and mullite into anorthite, which subsequently forms low-temperature eutectics and amorphous phases. A positive correlation was observed between Al₂O₃ content depletion in HACs and amorphous phase formation. Furthermore, depolymerization of the network structure of aluminosilicates in the ash, caused by the combination of SiO₂ and CaO in the low-AFT coal, favored the lowering of the AFTs. The interactions and melting processes of blended coal ashes involved three stages: shrinkage, infiltration, and diffusion. The difference in the temperature span of each stage for the HAC ashes was attributed to the formation temperature and content of mullite.</p>