Hydrothermal dewatering (HTD) was employed to dry and upgrade Inner Mongolia brown coal (IM) in an autoclave reactor at temperatures between 200 and 320 degrees C. It was found that the extent of decrease of moisture content and decomposition of oxygen functional groups in brown coal during HTD depended on temperature increase. X-ray photoelectron spectroscopy results showed that the proportion of carboxyl decreases from 16.57% to 4.38% and carbonyl decreases from 19.52% to 5.4% following the HTD process at 320 degrees C, and there was hydroxyl produced at low temperature that decomposed at high temperature. Liquid products from HTD were found to contain organic carbon ranging from 0.367 g/L at low temperature to 4.792 g/L at high temperature. Larger numbers of cations and anions were dissolved into the liquid product and reduced the surface tension. Preparing the liquid and solid products of HTD for coal water slurry (CWS) could recover the energy and get rid of wastewater effectively. The fixed-viscosity concentration of CWS increases from 44.4% for raw coal to a maximum of 59.1%. Those CWS also have a good rheological behavior and static stability.