Abstract: In order to obtain the molecular structure of sulfur and nitrogen compounds in the aromatic fraction of coal liquefaction heavy oil,the aromatic fraction of coal liquefied heavy oil was characterized at the molecular level by using ultra-high resolution electrospray ionization source combined with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The molecular composition of sulfur and nitrogen compounds in the aromatic components of coal liquefaction heavy oil is relatively complex. The elemental compositions of 826 kinds of basic nitrogen compounds,481 kinds of neutral nitrogen compounds and 333 kinds of sulfur compounds were identified by ESI FT-ICR MS. Five kinds of basic nitrogen compounds with different molecular compositions were identified in positive ion ESI mode,two kinds of sulfur compounds were identified combined with methyl derivatization,and six kinds of neutral nitrogen compounds were identified in negative ion ESI mode. The highest relative abundance of basic and neutral nitrogen compounds were both N1 compounds,and the highest relative abundance of sulfur compounds were S1 compounds.Through the analysis of the equivalent double bond number (DBE) and carbon number distribution of various compounds,important information about the molecular composition of the aromatic sulfur and nitrogen compounds of the coal liquefaction heavy oil was obtained. The main core structures of the basic N1 class species were quinoline and acridine,the alkyl side chains were mainly C8-C17 and C6-C11 ,and the neutral N1class species was carbazole with C9-C14 alkyl side chain. The degree of condensation and carbon number distribution of N1 basic compounds were greater than those of N1 neutral compounds,which makes it more difficult to remove basic N1 compounds than neutral N1 compounds during hydrogenation. The main core structures of S1 sulfur-containing compounds were dibenzothiophene and naphthobenzothiophene,and the alkyl side chain length was C1-C8. In addition,it was a highly condensed thiophene compound containing 4 to 6 benzene rings.