The invention belongs to the field of vacuum heat insulation boards, particularly relates to a core board material of a vacuum heat insulation board for buildings and aims at the problems that existing core materials do not have excellent pressure resistance stability and heat insulation stability, and are higher in heat conductivity, high in cost and difficult to process, and thermal inertia andheat insulation fail to meet strict requirements. The core board material is prepared from the following raw materials in parts by weight: 23-26 parts of mineral wool, 18-22 parts of glass fiber, 22-26 parts of silica, 14-18 parts of calcium chloride hexahydrate, 8-12 parts of quicklime, 6-9 parts of acrylic acid, 7-11 parts of polyvinyl alcohol, 4-8 parts of potassium hydrogen sulfite, 13-16 parts of bentonite, 11-14 parts of quartz sand, 9-13 parts of magnesium oxide, 5-8 parts of zinc oxide and 30-35 parts of deionized water, wherein rock cotton fiber accounts for 20-25 parts of the mineralwool. A preparation method of the core board material comprises the following step: S1, adding acrylic acid and deionized water to a reaction kettle. The core board material has excellent pressure resistance stability and heat insulation stability, low heat conductivity, high hardness, excellent thermal inertia and heat insulation effect and low manufacturing cost, and is convenient to process.