The ash fusion temperatures (AFTs) of 21 typical Chinese coal ash samples and 60 synthetic ash samples were measured in Ar and H-2 atmospheres. The computer software package FactSage was used to calculate the temperatures corresponding to different proportions of the liquid phase and predict the phase equilibria of synthetic ash samples. Empirical liquidus models were derived to correlate the AFTs under both Ar and H-2 atmospheres of 60 synthetic ash samples, with their liquidus temperatures calculated by FactSage. These models were used to predict the AFTs of 21 Chinese coal ash samples in Ar and H-2 atmospheres, and then the AFT differences between the atmospheres were analyzed. The results show that, for both atmospheres, there was an apparently linear correlation and good agreement between the AFTs of synthetic ash samples and the liquidus temperatures calculated by FactSage (R > 0.89, and sigma < 30 degrees C). These models predict the AFTs of coal ash samples with a high level of accuracy (SE < 30 degrees C). Because the iron oxides in coal ash samples fused under a H-2 atmosphere are reduced to metallic iron and lead to changes of mineral species and micromorphology, the AFTs in a H-2 atmosphere are always higher than those with an Ar atmosphere.