ChCl/C6H8O7 deep eutectic solvent(DES) was synthesized by choline (ChCl) as hydrogen bond acceptor and citric acid (C6H8O7) as hydrogen bond donor. Meanwhile, twenty percent of water was added into ChCl/C6H8O7 to reduce the viscosity. The structure was characterized and analysed by FI⁃IR and 1H⁃NMR. The denitrification of basic nitrogen in simulated oil was studied by using ChCl/C6H8O7 DES as extractant. The results show that the removal rate of quinoline in the simulated oil can attach to 95.64%, when the mass ratio of solvent to oil is 1∶5, the extraction time is 35 min, and the extraction temperature is 20 ℃. At the same time, taking toluene and cyclohexene as examples, the effects of aromatic hydrocarbons and olefins on the denitrification of DES are investigated. The mechanism of denitrification of DES is determined by infrared spectroscopy