Abstract Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are an important group of components produced from the thermal conversion of cellulose. Through using gas chromatography mass spectrometry (GC–MS), Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) and ultraviolet fluorescence spectroscopy (UV-F), the information for the evolution of OPAHs is obtained in this study. The tar produced at low temperature mainly contains light components such as homologues of pyran and furan, while the components in the tars at 700 °C and 900 °C show high double bond equivalent (DBE) values, indicating the existence of large aromatic structures. High temperature promote condensation reactions during cellulose thermal conversion, thus leading to a higher percentage of OPAHs in the tar at higher temperature process. According to Density Functional Theory (DFT) calculation, the energy barrier of Diels-Alder reaction (302.65 kJ/mol) is lower than the dehydration (583.26 kJ/mol), which means that Diels-Alder reaction could be the main route for OPAH formation rather than dehydration reaction. High reaction temperature is calculated to be favorable for the formation of naphthol during the cellulose thermal conversion because of the high energy barrier of dehydration between phenol and furan. It is consistent with the ESI FT-ICR MS result that there is a higher content of naphthol in the tar at 700 °C than that at 500 °C.