Abstract: The size of coal sample reaction chamber had a significant impact for the test results of small coal low temperature oxidation test furnace. By Fluent simulation technology, it simulated the characteristics of the flow velocity distribution and oxygen dissipation distribution in the coal mine reaction chamber with different diameter. The results showed that the gas flow velocity was proportional to the diameter of the reaction chamber when the gas flowing through the coal samples; the oxygen consumption of coal samples was inversely proportional to the diameter of the reaction chamber; compared to the reaction chamber diameter of 37mm and 65mm, the reaction of coal and oxygen was more uniform for the reaction chamber with 45mm diameter. By numerical calculation, it obtained the oxygen consumption rate of Antaibao lignite in the reaction chamber of different dimensions at 70 ℃, which verified that the oxygen consumption of coal samples was inversely proportional to the diameter of the reaction chamber.