Abstract: Thermal filtration of coal tar was carried out on two kinds of filter with the precision of 2-5 μm and 20- 40 μm,respectively,and quinoline insolubles (QI) was extracted from the filtration residue. Then the composition and structure of these of QI were analyzed by EA,LPSA,SEM / EDS,FT-IR,XRD and XPS,and so on. The results show that the QI components in coal tar had a high degree of aromatization and a lot of polycyclic aromatics with a lot of side chains or hetero atoms as well as a small amount of SiO2 ,CaCO3 ,coal ash,etc. when the low precision filter was used, the polycondensation of QI was much higher,and the condensed ring structure contained less side chains and lower heteroatoms. Meanwhile,the metal heteroatoms in the extracted QI components were relatively high,and these metal heteroatoms mainly presented in the large particles of inorganic matter and partly in the small particles of organic mat-ter. However,when a high precision filter was employed,the QI components mainly contained phenols,ethers and car-boxylic acid organic matter and fewer ketone;on the contrary,QI contained more phenols,ethers and ketones. In conclusion,the precision of filter should not be used too high,especially for the filter precision under 5 μm during a coal tar thermal filtration process.