In this study, hydrothermal liquefaction (HTL) of corn straw at different operation temperatures, reaction time and catalyst dosage were investigated, and the main product was heavy bio-oil. Results showed that CuO + NaOH have a synergistic effect in the HTL of corn straw. The product distribution and composition were also studied during the process, in which aromatic compounds achieved the highest proportion in heavy bio-oil. Moreover, the yield of aromatic compounds in hydrothermal products increased under simultaneous action of homogeneous and heterogeneous catalysts. The maximum ratio of aromatic compounds was 89.84% under condition of temperature 230 °C, reaction time 1 h, CuO content 3 g and NaOH 100 mL (1 mol·L). GC-MS analysis indicated that the major organic compounds in heavy bio-oil at temperatures between 210 °C and 270 °C were interestingly similar. SEM, XRD, H-TPR and XPS analysis showed that CuO was completely reduced to copper in the process.