The hydrothermal carbonization of biomass has aroused great interest within the context of global climate change. However, there is little information available on the composition of the liquefied products. In this paper, the intermediates in liquid phase from the hydrothermal carbonization of Camellia Oleifera shell (COS) were analyzed with gas chromatography - mass spectrometer (GC - MS), and the possible conversion pathways of COS were also explored. Under the hydrothermal conditions of 230 ℃ and 12 h, the main intermediates detected in the liquid phase included acyclic compounds, phenolic compounds, and cyclic compounds. Most of these compounds, such as furfural, dimethoxy phenol, p -methoxyphenol, phenol, lactic acid and levulinic acid, etc. were recognized by the NIST Library for GC -MS. Based on the fact that the main components of COS are cellulose, hemicellulose and lignin, it could be speculated that the cellulose and hemicellulose in COS were degraded into carbohydrates, which were then converted into furan derivatives, cyclic compounds, short-chain alcohols and short-chain organic acids by the reactions of isomerization, bond breaking and dehydration. The lignin and tannin in COS were converted into phenol and methoxyphenol.