Variations of gas products and reaction characteristics of main functional groups during low-temperature oxidation of coals with different metamorphic degrees were analyzed based on the gas chromatographic analysis of gas products and the FTIR determination of oxidized coal samples. Meanwhile, changes in the microcrystalline structure parameters during the low-temperature oxidation were determined with the aid of the XRD technology. Since gas product contents of coal with different metamorphic degrees grow continuously with the rise of oxidation temperature, a forecast system that adopted CO and C2H4 as indicator gases in the low-temperature oxidation process was established. The content of -CH3/-CH2-, the primary participant in the oxidation reaction, gradually falls with the rise of oxidation temperature. During the low-temperature oxidation of coal, the stacking height L-c, ductility L-a, stacking layer N and graphitization degree P of aromatic layers all increase with the rise of oxidation temperature. Finally, the critical temperature ranges (80-110 degrees C for RL coal, 110-140 degrees C for YL coal and 130-170 degrees C for WY coal) for drastic changes during low-temperature oxidation were proposed by comparatively analyzing the variation laws of gas products, main reaction functional groups and aromatic layers, as well as the corresponding temperature variations.