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It is difficult to obtain comprehensive information on coal pyrolysis with a single analytical tool due to the diversity of coal pyrolysis products. Low-temperature pyrolysis of coals with three ranks was characterized by online analytical methods to accurately explore pyrolysis mechanisms. Thermogravimetric (TG) analysis was used to characterize the basic pyrolysis characteristics of the coals. In-situ pyrolysis technique combined with gas chromatography-mass spectrometry (Py-GC/MS) and pyrolysis synchrotron radiation vacuum ultraviolet photoionization time-of-flight mass spectrometry (Py-SVUV-PI-TOF-MS) were employed in explaining the mechanism of coal pyrolysis at low temperature. The temperature of macromolecules fragmentation increases with coal rank, and a higher coal rank leads to aromatic products with a larger ring size. Different trends of adsorbed substances in coal pores with coal rank and the corresponding pyrolysis products were analyzed by Py-SVUV-PI-TOF-MS. The peak area of ethanol decreased with increasing temperature, while the pyrolysis products increased. By combining Py-GC/MS and Py-SVUV-PI-TOF-MS, possible coal macromolecular structures were obtained by reverse extrapolation of the pyrolysis products. • Two on-line MS techniques were used to characterize pyrolysis products of coals. • The fracture temperature of the coal structure is obtained by Py-GC/MS. • Adsorbed gases and pyrolysis products are distinguished by Py-SVUV-PI-TOF-MS. [ABSTRACT FROM AUTHOR]