The effluent of food waste (FWE) is generated during food waste treatment process. It contains high organic matter content and is difficult to be efficiently treated. In this study, the sample was collected from a 200 t/d food waste treatment center in Hangzhou, China. Subcritical and supercritical water gasification were employed to decompose and convert FWE into energy. The effects of reaction temperature (300–500 °C), residence time (20–70 min) and activated carbon loading (0.5–3.5 wt%) on syngas production and the remaining pollutants in liquid residue were investigated. It was found that higher reaction temperature and longer residence time favored gasification and pollutant decomposition, resulting in higher H₂ production and gasification efficiencies. It is noteworthy that the NH₃-N was difficult to be converted and removed under current experimental conditions. The addition of activated carbon was found to increase the gasification efficiency. The highest total gas yield, H₂ yield, carbon conversion efficiency, gasification efficiency, total organic carbon removal efficiency and chemical oxygen demand removal efficiency were obtained from gasification at 500 °C for 70 min with 3.5 wt% activated carbon.