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A molecular level characterization method for investigating composition and structure of medium and low temperature coal tar derived from Inner Mongolia lignite upgrading plant has been developed in this paper. The physical and chemical properties of medium and low temperature coal tar was described from macro level. The medium and low temperature coal tar and its chemical composition under different distillation ranges and subcomponent of different natures was investigated from molecular level. Firstly, the whole fraction of medium-low temperature coal tar was separated into 16 narrow fractions by real boiling distillation, and analyzed on their properties. Secondly, the acidic fraction, the alkaline component and the neutral component were separated by acid-base extraction for the >180 °C heavy fraction, and the neutral component was separated on the extraction chromatographic apparatus to obtain six characteristic subcomponents. The compositions and molecular structures of full-range fractions, narrow fractions and sub-fractions were analyzed by GC/MS. Results show that the water content of all coal tar fraction is 28%, at 20 °C, the density is 1003. 7 kg/m3, the oxygen content is 7.4%, and the fraction content( <180 °C) is 14.24%, and the fraction content( <360 °C) is 63.4%. This indicates that it is a typical medium and low temperature coal tar. The molecular compositions of light fractions( <180 °C) mainly comprise benzene, toluene and xylene, with some small molecular alkanes and olefins. In heavy distillate( >180 °C), acidic compound accounts for 27.6%, basic component 2.46%, neutral component69. 94%. In neutral components, Saturation is 33.60%, aromatic 38.70%, gelatine 25.10%, asphaltene 2.60%. The intermediate and heavy fractions also contain a large number of phenolic compounds, with aromatic hydrocarbons as main molecular structure, and long-chain n-alkanes as well. Medium and low temperature coal tar contains a large number of oxygenated compounds, mainly phenolic compounds, alkyl phenols, which are relatively abundant at 160-280 °C, and also contains a few number of ketones. [ABSTRACT FROM AUTHOR]