The invention relates to an extractant for extractive rectification of m/4-ethyltoluene from a C9 aromatic hydrocarbon mixture and a separation method, and mainly solves the technical problem of difficult separation of m/4-ethyltoluene from a C9 aromatic hydrocarbon mixture. According to a technical scheme, salicylate and/or maleic acid diester are/is adopted as the extractant, the C9 aromatic hydrocarbon mixture is introduced into a heavy component removal tower equipped with a liquid accumulation tank at the tower top to conduct batch rectification, 1, 2, 4-trimethylbenzene and 1, 2, 3-trimethylbenzene are extracted from the column bottom, the tower top stream is introduced into an extraction rectification tower to perform extraction rectification, m/4-ethyltoluene is extracted from the tower top, the column bottom stream enters a solvent recovery tower, o-methylethylbenzene and mesitylene can be obtained at the tower top, and the combined extractant can be obtained at the column bottom. The extractant and the separation method provided by the invention well solve the problem, and can be applied to the field of C9 aromatic hydrocarbon mixture separation.