The invention relates to a method for preparing superfine molybdenum powder by reducing carbon-magnesium, and belongs to the field of ultrafine metal powder preparation. According to the method, the method for preparing superfine molybdenum powder by reducing the carbon-magnesium is characterized in that two solid reducing agents such as carbon and magnesium are used, and a raw material of molybdenum dioxide or molybdenum trioxide is reduced into molybdenum powder in two stages; the method comprises the following steps that in the first reduction stage, the carbon is used as a reducing agent for reduction, carbon ratio at this stage is required to be insufficient so as to obtain the extremely low carbon content in an obtained pre-reduced molybdenum powder; in the second stage, the productobtained in the first stage is mixed with the magnesium and magnesium chloride under a certain temperature to react, the residual oxygen is removed, the product obtained after reaction is subject to acid leaching to remove magnesium oxide and the magnesium chloride, so that the degree of the molybdenum powder of the final product is guaranteed. By using the method, the obtained product particles are small; the molybdenum powder particles obtained in the carbon reduction stages are about 0.3 micron to 0.6 micron, and the product particles obtained in the magnesium reduction stage are smaller inparticle size and are about dozens of nanometers, so that preparation of the molybdenum material or the molybdenum alloy subsequent powder metallurgy is more facilitated; in addition, equipment usedby the method is simple, the technological process is easy to operate, the cost is low, and the method is suitable for industrial production.