In response to increasing energy demands and the inevitable release of greenhouse gases into the environment, researchers have turned their attention to biomass energy production. Biomass offers a lot of benefits; however, it has poor calorific value due to its higher moisture and volatile content. Carbonization can be used to overcome this disadvantage and produce biomass with a higher carbon content. One of the most promising thermochemical conversion techniques is gasification. In this study, biochar from oak wood was gasified in a steam environment using Aspen Plus® simulation. The downdraft gasifier model was developed under steady-state equilibrium parameters based on the minimization of Gibbs free energy. As consistent with the literature, H2 was produced higher amount in the steam gasification (55.65%) compared with the air gasification (17.36%). Parametric analyzes were performed to investigate the influence of the operating parameters on the composition of the syngas. Results depicted that the increasing temperature and steam/biochar ratio raised the H2 concentration from 53.21% to 55.72% and 54.50% to 56.84% in syngas respectively. Temperature also showed positive influence on the LHV of syngas that changed between 19620-19708 kJ/kg. The steam/biochar ratio affected the LHV of syngas negatively thus it decreased from 20257 to 18777 kJ/kg.