Dewatering and upgrading of Yunnan brown coal in non-polar solvent (tetrahydronaphthalene, THN) were carried out at mild conditions with bench-scale apparatus, and the resultant samples were separated from the slurry and analyzed with Fourier transform infrared spectroscopy (FTIR), C-13 nuclear magnetic resonance (C-13 NMR) and thermo-gravimetric analyzer coupled with mass spectroscopy (TG-MS) to explore the structure changes and variance of pyrolysis reactivity that introduced in the treatment. The results show that the solvent treatment is effective in dewatering and upgrading of Yunnan brown coal. Carboxyl groups and C-O bonds in ethers, esters, alcohols start decomposing at 150 and 200 degrees C, respectively, while the aliphatic, aromatic structures as well as phenolic groups remain relatively stable below 300 degrees C. The coal structure becomes more associated and compact after the solvent treatment, and the pyrolysis reactivity of the treated sample is slightly lower than that of the raw coal. (C) 2014 Elsevier Ltd. All rights reserved.