Composition analysis of coal tar remains a challenging task because of its complex components. In this paper, the compositions of low temperature coal tar (LTCT) and the wash oil fraction of high temperature coal tar (HTCT) were studied. A thermogravimetric analyzer (TG) combined with gas chromatography-mass spectrometry (GC/MS) with the same temperature program was put forward to analyze the quantitative determination of the GC/MS analyzable part of coal tar, and the composition and distribution of the GC/MS unanalyzable part (300LTCT and 300HTCT obtained from TG at the final temperature of 300 degrees C) was investigated by a pyrolysis gas chromatography mass spectrometer (Py-GC/MS). Results reveal that light compositions can be extracted by petroleum ether (PE) more effectively than heavy compositions. PE soluble fractions of LTCT and HTCT cannot be totally gasified by GC/MS, and the remaining parts at above 300 degrees C are 6.51 wt % and 4.99 wt %, respectively. GC/MS combined with TG can accurately analyze the composition of <= 300 degrees C fractions in coal tar. Four dehydrogenation reactions were presented in the fast pyrolysis process of coal tar. An intermolecular association occurs in 300HTCT. 300LTCT is mainly composed of phenols, aliphatics, and aromatics. The composition analysis of 300LTCT and 300HTCT by Py-GC/MS indicates that there are some bridge bonds in the macromolecular structure of coal tar, and they have broken down to produce small molecular weight of phenolic compounds and aromatic hydrocarbons during pyrolysis.