In order to obtain a detailed understanding of the effect of reaction atmospheres on the sintering temperature of coal ash under elevated pressure (0.7-1.0 MPa), a series of experiments have been conducted on the pressurized pressure-drop measuring device, together with analyses using X-ray diffractometer (XRD) analyzer. The results show that the sintering temperatures decrease under the single gas and the atmospheres of mixed reaction gases with increasing in pressure (0.1-1.0 MPa). However, the extent of the decrease is not obvious in the pressure range from 0.7 to 1.0 MPa. The sintering temperatures of coal ash under the reducing reaction atmospheres (H-2, CO and gasification atmosphere) are lower than under oxidizing atmospheres (N-2, O-2, CO2 and combustion atmosphere). In addition, the XRD patterns show that some minerals in coal ash, such as muscovite and anhydrite, are present as fluxing minerals that can reduce the sintering temperatures; while some feldspar minerals may react with other minerals to produce the low temperature eutectics with the rise in pressure, thus reducing the sintering temperatures. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.