A polyether amine (PEA)-based solvent, which can be synthesized by PEA and formic acid (FA), is a green, low-cost, and efficient extractant for desulfurization and denitrogenation. Under the conditions of ambient pressure, 15 min, 30 degrees C, m(extractant)/m(oil) of 1:1, and n(FA)/n(PEA) of 10:1, S removal of dibenzothiophene (DBT), benzothiophene (BT), and thiophene (T) was 72.16, 63.96, and 53.01%, respectively, and N removal of indole, pyrrole, pyridine, and quinoline was 98.31, 97.12, 91.51, and 89.93%, respectively. The activity of the PEA/FA complex was attributed to an active O atom originated from PEA and an amide group formed by the reaction and the complexation between PEA and FA, which was beneficial to enough Lewis basicity and mild Bronsted acidity. In addition, the PEA/FA complex can realize deep desulfurization by multi-stage extraction and has good regeneration ability. The PEA/FA complex was still effective for real oil. More than 68% of sulfur in straight-run diesel oil can be removed after 5 cycle extractions.