Abstract: In order to study the variation features of the functional group in the middle and high rank coal, 10 coal samples with different metamorphic grades were collected from the north part of Qinshui Basin as the study objects. A Fourier transform infrared spectrometer was applied to the infrared spectrum analysis on the coal samples. With the peak sharing fitting of the FTIR curves, the relative contents of the aliphatic structures, oxygen functional groups and aromatic structure could be obtained. The study results showed that in the middle and high rank coal, the content of the aliphatic structures would be low. The aromatic rings with only one adjacent hydrogen atom was the main aromatic structure,and showed that the aromatic structures had a high substitution.In the oxygen functional group, the ether oxygen would steadily became the oxygen functional group with a high content and indicted a high stability of the oxygen atom existed with the ether oxygen mode. With a test conducted on the maximum reflectance Rmax of the vitrinite in the coal samples, the infrared structure parameter and the Rmax relevance of the coal samples were discussed. The test showed that with the Rmax(1.1%～2.7%) increased, the aromaticity would be increased, the condensation degree of the aromatic structure would be increased and the ‘A’ factor of the reactive hydrocarbon potential would be decreased. Thus the results of the coalification at this stage would have more increased aromatic hydrocarbons.