A new supercritical water process for biomass waste gasification and copper recovery was designed and investigated. In this research, cornstalk depolymerization residual as biomass waste and simulated copper wastewater were treated simultaneously in a batch reactor at 650 degrees C and 22.5 MPa. The amount of copper ions has a significant effect on the biomass waste gasification. The carbon gasification efficiency reached 99.2%, and the gas products were mainly CO2 when 2.5 mmol of copper ions were added to 0.1 g of dried biomass waste. Moreover, the solid products were confirmed to be copper and cuprous oxide nanoparticles, and the copper recovery reached 99.9%. During this process, the cornstalk depolymerization residual was oxidized and the copper ions were reduced without additional oxidizing agents and catalysts. The synergetic effect of wastewater treatment could be used for the gasification of the biomass waste and the effective removal of heavy metal ions.