A simple, efficient and green method has been developed for the synthesis of benzothioamide from benzonitrile in supercritical CO2, which could be used to synthesize various benzothioamide derivatives efficiently without organic solvent. Notably, some sulfur-containing ionic liquids were prepared and they could promote the thiolysis of benzonitrile to produce benzothioamide in an excellent yield. Moreover, the investigation on the reaction mechanism showed that the acid-base property of the reaction solution was key to the thiolysis of benzonitrile mediated by the sulfur-containing ionic liquids.