Abstract: The carburizing reaction of molybdenum trioxide was investigated in CH4/H2 mixture using insitu TG-DTA. The effects of ramping rate and carburization temperature on the carburizing reaction of molybdenum trioxide were also studied. The results indicate that molybdenum carbide can be prepared by temperatureprogrammed reaction(TPR) to carburize molybdenum trioxide through the pathway of MoO3→MoO2 →MoOxCy→Mo2C under CH4/H2 atmosphere at ramping rate of 1℃/min with the optimal carburization temperature of 675℃. When the ramping rate is above 2℃/min，the carburizing reaction process of molybdenum trioxide changes to MoO3→MoO2→Mo＋MoOxCy→Mo2C. In the mean time, the amount of Mo element generated in the second weight loss stage increases with the increase of the ramping rate. The beginning and the finishing temperature of carburizing reaction also increase with in the increase of the ramping rate. Despite the fact that the carburizing reaction pathway of MoO3 in CH4/H2 mixture is similar in a range of carburizing temperatures, high reaction temperature could lead to the coking reaction of the hydrocarbon and deposit of free carbon on the catalyst surface, which could induce the BET surface area decrease and hence reduce the catalytic activity of the Mo2C.