Gasification of petrochemical wastewater for hydrogen production in supercritical water was studied in a fluidization bed system with the presence of Na₂CO₃ and K₂CO₃. The influences of the main parameters, including temperature, pressure, feedstock concentration, and catalyst addition, on the gasification process were discussed. Experiment results show that temperature is the key factor and pressure has a minor effect on petrochemical wastewater gasification. Higher temperature and pressure favors petrochemical wastewater gasification. Gasification performance of petrochemical wastewater decreases with increasing concentration. Gasification efficiency increases and molar fraction of CO decreases with Na₂CO₃ and K₂CO₃ addition. It is implied that the supercritical water fluidization bed system is effective for hydrogen production by biomass gasification.