The invention relates to a nano heat-insulating material and a preparation method of a nano heat-insulating board. The nano heat-insulating material has the characteristics of high temperature resistance, high heat stability in the medium/high-temperature state, low thermal conductivity and low cost. The preparation method provided by the invention has the advantages of accessible raw materials, simple technique and convenient preparation process. The technical scheme is as follows: the nano heat-insulating material is prepared from common silicon micropowder, white carbon black, refractory fibers, an organic adhesive and water. The preparation method of the nano heat-insulating board sequentially comprises the following steps: preparing the following raw materials: common silicon micropowder, white carbon black, refractory fibers, organic adhesive and water; 1. crushing the refractory fibers for later use; 2. preparing the organic adhesive liquid for later use; 3. mixing the crushed refractory fibers, common silicon micropowder and white carbon black, and stirring for 20-30 minutes to obtain a mixture; 4. preparing the nano heat-insulating board with different specifications; 5. spraying the organic adhesive liquid onto the external surface of the nano heat-insulating board; 6. drying; and 7. cooling and packaging.