To simultaneously produce synthetic natural gas (SNG) and char from biomass, this paper proposed a novel cogeneration process via pyrolysis-coupled hydrothermal gasification. Two typical process configurations were designed and modeled by Aspen Plus. A mathematical model of bio-oil composition involving varieties of typical organic components was established by digging experimental data and then integrated into the Aspen Plus platform, which can describe the biomass pyrolysis process better. Taking SNG as the main product, this work focused on the effects of pyrolysis temperature, hydrothermal gasification temperature and pressure, and feedstock concentration on the composition and yield of SNG as well as energy efficiencies. The results show that the pyrolysis temperature significantly affects the yields of SNG and char, as well as energy efficiencies. Subsequently, the composition and yield of SNG are quite sensitive to the hydrothermal gasification temperature. Then, the hydrothermal gasification pressure has little influence on all process indicators. Finally, the feedstock concentration only has a small effect on CH4 concentration and SNG yield. By application of the flexible operation modules of the cogeneration process, biooil can be potentially used as the carrier for seasonal energy storage. This cogeneration process can be regarded as a new approach to upgrade and utilize raw bio-oil.