In this study, the water-soluble products formed during the hydrothermal carbonization of glucose were analyzed by liquid chromatography (LC)-mass spectrometry (MS) and LC-MS2 to determine the formulas and the possible structures of the main compounds. In addition to the well-known compounds of 3-deoxyglucosone, 5-hydroxymethylfurfural, and levulinic acid, the furanic compounds and the carbocyclic oxy-organics containing hydroxy group and carbonyl group with a molecular mass range between 170 and 260 Da were also identified. Both C-C coupling reaction and C-C cleavage reaction were proved to be involved during the formation of these carbocyclic oxy-organics, so they were proposed to be released via C-C cleavage of the primary polymers, which were formed by aldol condensation of the primary precursors formed during the degradation of glucose. The identification of these carbocyclic oxy-organics was indirect evidence that aldol condensation played a crucial role during the formation of hydrochar from carbonization of glucose.