In the process of coal gasification, the inorganic components of coal ash will be pyrolyzed, agglomerated or slagged in a short time, which seriously affects the safe and stable operation of gasifier. In order to explore the melting process of coal ash staying in gasifier and the transformation behavior of coal ash minerals, XRF, XRD, FTIR and other test methods and FactSage sofeware were used to analyze the chemical composition, mineral composition and melt structure of coal ash treated at different temperatures and time spans. The results show that under the conditions of 1 200, 1 300 and 1 400 ℃, when the constant temperature time gradually increases from 10 s to 30 min, the mineral type in coal ash has no obvious change, while the proportion of SiO2, CaO and SO3 in coal ash has a great change. The amorphous substance of mineral increases with the increase of temperature and the extension of constant temperature time. At the same time, the structure of ash melt is gradually depolymerized from complex frame structure to simple ring, island and other structures. The viscosity of coal ash also decreases gradually with the increase of temperature. After reaching the turning point of 1 240 ℃, temperature and constant temperature time have little influence on melting behavior of coal ash melt.