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Hemicellulose, cellulose and lignin are the main components of biomass. Different structures and components of the three components may have important effects on the product properties and reaction process of biomass hydrothermal carbonization. However, in the past few years, there were limited reports on HTC of xylose and its effect on the structure changes of cellulose and lignin during HTC. In order to study the hydrothermal carbonation characteristics of xylan, hydrothermal carbonation experiment was carried out in the batch reactor at 160~240℃ for 120min. The effects of xylan on the hydrothermal process of cellulose and lignin were investigated at 220℃ for 120min. It was found that the xylan hydrochar appearred at 200℃, and its yield was gradually increased with the increase of reaction temperature. When the temperature reached 240℃, the yield reached 13%. Xylose was also mixed with cellulose and lignin respectively according to the proportion of three components in wheat straw, and the mixture was hydrothermally treated at the temperature of 220℃ for 120min. The results showed that xylan had little effect on the yield of cellulose hydrochar, while the carbon mass fraction was increased from 42% of the cellulose hydrochar to 48% of the cellulose and xylose hydrochar. The yield of xylan and lignin hyrchar was decreased by 23 percentage points and the carbon mass fraction changed little compared with those of lignin hydrochar. The functional groups were decreased with the increase of temperature, while the C=C, C=O and aromatic peaks were gradually enhanced, and the thermogravimetric analysis presented a good thermal stability of xylan. Fourier transform infrared spectroscopy, X-ray diffraction analysis and thermogravimetric analysis showed that xylan can promote the fracture, polymerization and aromatization of the molecular structures for cellulose and lignin during hydrothermal carbonization, and improve the aromatic properties of hydrochars.