The invention relates to a method for preparing molybdenum pentachloride, which belongs to the technical filed of inorganic chemistry. The method comprises the following steps of: firstly blending molybdenum trioxide and dehydrated carbon tetrachloride in mass ratio of 1:4-1:6 in a round-bottom stainless steel reaction bulb, and closing a valve for sealing after the reaction bulb is degassed; then completely immerging the reaction bulb into an oil bath pan and heating to 150 DEG-240 DEG, keeping the temperature for 1-12 hours, and taking out the reaction bulb after cooling; and at the moment,with the change of a reaction solution color from original colorlessness to brownish red and the precipitation of black acicular crystals, opening the valve of the reaction bulb to discharge reactiongas, pouring the reaction solution into an evaporator, and evaporating to remove the carbon tetrachloride to obtain black molybdenum pentachloride crystals. The method has the advantages of simple and easily-controlled technology, high production efficiency, lower raw material price, simple production condition, low production cost, single product phase structure and high purity, and because the reaction is carried out in a sealed system, less pollution is generated.