The utility model relates to a reduction furnace device for vacuum-thermal reduction of metallic magnesium, which belongs to the field of metallurgical equipment. The reduction furnace device is characterized in that two ends of the reduction furnace device are positioned outside; the middle of the reduction furnace device is reduced, i.e., reduction materials are formed, dehydrated, dried and loading carbonized (curing) and towed outside a reduction furnace and enter the vacuum reduction furnace; the reduction materials are subjected to carbon thermal reduction in the vacuum environment in the furnace that the temperature is 1,100-1,550DEG C and the pressure intensity is 1-330Pa to form magnesium steam; a condensing crystallization tank outside the furnace forms a quenching environment under the action of a vacuumizing system and a water circulating system, so that the magnesium steam is condensed and crystallized in the condensing crystallization tank to form solid metallic magnesium; a crystallization tank in the condensing tank is mechanically detached and is simultaneously replaced by a new tank and closed in time; and a crude magnesium crystallization tank is mechanically detached, a thick mechanical jack is pushed out of the crystallization tank, the refining is carried out in a refining furnace, waste slag loaded in a reduction vehicle is transported to the outside of the furnace through a towing device, the circulation is repeated and the intermittent production is carried out.