Abstract: Hydrothermal carbonization（HTC）experiments of de-ashing rice straw were carried out. Rice straw as reference,the chemical structure and combustion properties of the hydrochar were investigated using the Fourier transform infrared spectrum and the Thermogravimetric analyzer. The results indicated that the hydrochar yield gradually decreases from 70.9% to 36.2%,while the carbon content increases from 42.03% to 63.33% with reaction temperature increasing from 150 ℃ to 300 ℃ for 240 min. Compared with the yields and carbon content of the hydrochar from the rice straw,the values of the hydrochar of the de-ashing rice straw are high,however,the gap between the two gradually decreases. The infrared absorption peaks of the C==O bond,aromatic ring skeleton vibration,and the functional groups representing polymer characteristics of the hydrochars from de-ashing rice straws are also stronger.Comprehensive thermogravimetric analysis shows that the de-ashing treatment decreases the diffusion resistance of water molecules in rice straw during hydrothermal process,reduces the low boiling point volatile matter,and increases the thermal stability of the hydrochar.