Abstract: To further understand the influence of coal particle size on the process of coal oxidation, the devices of blast oven and GC-950 gas chromatograph were applied to make a study of isothermal oxidation in closed space to measur variation of oxygen concentration with the change of time in coal samples reaction tank, and calculate and compare oxygen uptake rate of different particle size under the different temperature and time. Study shows that oxygen concentration affect oxygen consumption of different coal particle size. When oxygen is sufficient, oxygen consumption rate is increased with decrease of coal particle size, when oxygen is insufficient, oxygen consumption rate is in decline. Besides，there is negative index relationship between oxidation rate and oxidation time, and oxygen consumption rate of change decreases at first and then increases with decrease of coal particle size. When coal particle size is 1.00 to 2.00 mm,oxygen consumption rate of change is minimum and moxygen consumption rate reduces at the lowest rate.