The hot mixing chamber(HMC) is a device that mixes streams of fluid, to obtain gas with a pertinent operational temperature in the final outlet section which can meet the industry requirements. In this numerical simulation study, the flow and temperature characteristics in the hot mixing chamber in different cold air inlets conditions were obtained with aid of the software of FLUENT. The number of cold air inlets were 2, 3 and 4. For the 2 cold air inlets, there are 4 models with different inlet angles which are 90°, 120°, 150° and 180°. Therefore, totally 6 models including 3 air inlets angle of 120° and 4 air inlets angle of 90°, were simulated in this study. The simulation results showed the 3 cold air inlets model had the best performance for the highest temperature uniformity at the HMC outlet and the smallest wall temperature over the surface of the HMC.