This study experimentally investigated the influences of the varieties, granularity, moisture content, and loading density of biomasses on the steam explosion pretreatment effect. The steam explosion lasted for 120 s under pressure of 2.0 Mpa. The study results suggested that different biomass varieties show different sensitivities to the steam explosion treatment. The biomass with higher hemicelluloses content exhibited the optimum blasting effect. For corn straws, the reducing sugar yield and steam explosion treatment effect maximized at granularity of 20~30 meshes, with moisture content of 10%, and loading density of 80% respectively.