Abstract: The influence of pressure (0.1-6 MPa) on the mineral phase of coal char and the carbon crystal structure and the mineral conversion of coal ash were investigated by using the tube furnace at higher temperature and pressure combined with the analysis of X-ray diffractometer (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The results indicate that the mineral phase of coal char is not significantly affected by the pyrolysis pressure; while, the average stacking height or the graphitization degree of coal char increases with increasing the temperature and pressure. With respect to functional groups, the pressure has little effect on the structure of organic functional group. Also, it is found that the pressure has little effect on the main mineral phases of coal ash, but it can affect the relative contents of mineral phases, which is mainly due to the varying of combustion temperatures caused by the transition of the ignition mechanism at different pressures. The effect of temperature on the mineral transformation is more significant than that of pressure.