Abstract: Heat release characteristic of coal oxidation is one of the key factors influencing spontaneous combustion. To investigate the heat release characteristics of coal low-temperature oxidation under oxygen deficient atmosphere, by C80 calvet calorimeter, the heat flow of coal oxidation below 250 ℃ was tested under various atmospheres with 5%, 9%, 13%, 17%, and 21% oxygen concentrations. The initial temperature of heat release and quantity of heat release were analyzed. Furthermore, the apparent activation energy of coal oxidation was calculated. The results show that the initial temperature of heat release of coal fluctuates and increases with the decrease of oxygen concentration, while the intensity and quantity of heat release and apparent activation energy decrease. Moreover, there is a critical oxygen concentration, below which the heat release behaviors during coal oxidation will be inhibited obviously. There are two critical oxygen concentrations foreach of the tested coal samples, namely, 13% and 9%.