Abstract: Biomass is a zero-carbon emission renewable resource that is important for mitigating the greenhouse effect and solving the energy crisis. Pressurized combustion has received increasing attention due to its higher efficiency. Soot is inevitably generated during biomass combustion, which, as nanoscale fine particulate matter composed of polycyclic aromatic hydrocarbons (PAHs), not only reduces the combustion efficiency but also negatively affects the environment, human health, and climate change. However, there is a basic gap in the research on the characteristics of soot generation during biomass pressurized combustion. Pyrolysis is the initial stage of combustion. In this study, a pressurized fixed-bed reactor was used to investigate the soot generation characteristics during pressurized pyrolysis of straw. The experimental results show that the soot production from straw pyrolysis increases firstly and then decreases with the increase of pressure, and reaches the peak at 0.3 MPa. H2 production