To greatly save labor and time required for manufacture and repairing of a whole, to increase the heat insulation effect of a whole, and increase a working effect.

The inside surface and the bottom surface of the casing of a furnace body 1 are coated with one layer of a castable heat resisting material 12 in average. After the castable heat resisting material 12 is dried and solidified, the surface of the castable heat resisting material 12 is paved with heat resisting and having fire resistance in one layer. A precast heat insulation pot 4 is arranged on heat insulation sand, and a space formed between the outside of the heat insulation pot 4 and the castable heat resisting material 12 is continuously filled with the heat insulation sand to form one sand layer 3 at the periphery of the heat insulation pot 4. The surface of the sand layer 3 is covered with the heat resisting plate 6, the upper layer of the heat resisting plate 6 is covered with fire resisting fiber cotton 61, thus a molten metal heat insulation furnace is formed.