Stormwater from urban areas is often accompanied with a variety of chemicals such as heavy metals, phosphorus, trace organic and hydrocarbons. Thermal plasma under DC transferred mode was proposed for decontamination of sediment carried by urban stormwater. After dredging, stormwater sediment/sludge accumulated in a stormwater detention pond was spread on top of a filter and the residues were transferred to a thermal plasma reactor. The reduction of total organic carbon (TOC) is 22% on average. Sediment was melted into slag with thermal plasma treatment under DC partial transferred operating mode. After treatment, the major compositions of the original stormwater sludge (e.g. sand (SiO2) and calcite (CaCO3)) decreased while other compositions such as KAlSi3O8, Fe3O4, NaCl and CaSO4 were formed. The accumulated concentrations of CxHy, CO, CO2, NO, NO2, H2S and SO2 after a two-hour thermal plasma treatment were 6100, 10000, 6200, 9700, 140, 40 and 27 ppm, respectively.