Provided are a magnesium hydride preparation apparatus and a magnesium hydride preparation method. The magnesium hydride preparation device comprises: a transition chamber (1) comprising a feed port (11); a heating chamber (2) connected to the transition chamber (1) by means of a first valve (12); a heating device (6) having an upper end thereof provided with an opening, capably of moving between the transition chamber (1) and the heating chamber (2) by means of the first valve (12), and used for heating, in the heating chamber (2), the magnesium material placed therein; a collecting chamber (4) communicated with the heating chamber (2) by means of a pipe (3) so as to collect magnesium powder; and a reaction chamber (5) communicated with the collecting chamber (4) by means of a second valve (44) so as to receive the magnesium powder and communicated with an external hydrogen source so as to receive hydrogen. Magnesium powder preparation and hydrogenation are integrated in the magnesium hydride preparation apparatus. The magnesium hydride preparation method has simple steps, and the diameter of prepared magnesium hydride particles can be controlled within a range from 1 µm to 60 µm by controlling conditions such as a temperature and a pressure.