Abstract: A method characterization for the molecular structure of naphthenes in hydromodified light oil of direct coal liquefaction was established by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOF MS). The data collected by TOF MS were analyzed by comprehensively applying multiple qualitative methods, including spectral library searching, comparison of standard substances, retention index, spectrum analysis, comparison with standard mass spectra, analysis of the characteristics of comprehensive two-dimensional spectra, and extraction of characteristic ions of compounds. As shown by the results, the hydromodified light oil of direct coal liquefaction mainly contained 5 types of compounds, including alkane, monocyclic alkane, dicyclic alkane, alkyl benzene and monocyclic benzene. Naphthenes were mainly consisted of monocyclic alkanes and dicyclic alkanes. The monocyclic alkanes were mainly C1-C5 cyclopentanes with side chains, C1-C4 cyclohexanes with side chains, and C1 cycloheptane with side chains. The dicyclic alkanes were mainly a six-membered ring connected in series or in parallel with a five-membered ring, two six-membered rings connected in parallel, and two five-membered rings connected in series. In terms of relative content ( percentage of peak area in mass spectrometry), C8 compounds had the highest relative content in monocyclic alkanes, C9 compounds had the highest relative content in dicyclic alkanes.