The invention relates to an inorganic vacuum heat preservation plate for a building wall and a preparation method of the inorganic vacuum heat preservation plate, belongs to the field of heat preservation materials in building. The inorganic vacuum heat preservation plate for the building wall is formed in a manner that a condensate of the mixture of gas phased silicon dioxide powder and silicon carbide fiber is wrapped with a layer of compact low-melting-point glassy layer after being subjected to vacuum treatment. The preparation method of the inorganic vacuum heat preservation plate comprises the following steps: firstly, gas phased silicon dioxide powder and silicon carbide fiber are uniformly mixed, the mixture is compressed into the condensate, the condensate is vacuumized and is then wrapped with low-melting-point glass through liquid coating to form the inorganic vacuum heat preservation plate. According to the invention, the raw materials used by the inorganic vacuum heat preservation plate are noncombustible, stable and durable in chemical properties, so that the formed vacuum core sandwich structure has the advantage of low heat conductivity coefficient. The inorganic vacuum heat preservation plate for the building wall and the preparation method of the inorganic vacuum heat preservation plate, provided by the invention, can ensure that the vacuum heat preservation core materials can be kept in a vacuum drying stage for a long time in the preparation and usage process, therefore, the inorganic vacuum heat preservation plate provided by the invention has an excellent heat insulation property and excellent durability.