To investigate the characteristics of adiabatic oxidation reaction and predict critical temperature of coal spontaneous combustion, we carry out the adiabatic oxidation experiments of five coal samples and use the index of activation energy to reflect the characteristics of microcosmic reaction of spontaneous combustion in different stages. In addition, the critical point (T_c) is determined by using the F test of linear regression analysis. The results show that in the early stage of low temperature oxidation of coal, the values of activation energy range greatly, which indicates that reactions of the functional groups is very unstable at this time; as the temperature increases, the values of all samples are in a range of 55 to 70 kJ/mol in late period of the experiment, which indicates that the reaction has become relatively stable; T_c has good correlation with macro-heating rate, which indicates the model is scientific. In addition, T_c has linear relationship with t₀ (the time needed for spontaneous combustion temperature increasing to 160℃ in the experiment). Thus T_c could be predicted by t₀. This research could provide reference for the prevention fire and coal storage in mine.