The invention discloses a perlite heat preservation board and a preparation method thereof. The heat preservation board comprises the following raw materials: modified expanded perlite, kaolin, cement, plant ash, diatomaceous earth, sodium trimethylsilanolate, epoxy chloropropane, divinyl benzene, ethyl orthosilicate, N,N'-methylene bisacrylamide, calcium sulphate, sodium chloroacetate, sodium chloride, sodium silicate and water; and the preparation method includes the following steps: uniformly mixing the modified expanded perlite, the kaolin, the cement, the plant ash and the diatomaceous earth to obtain a mixture A; uniformly mixing the remaining raw materials, adding water, and performing stirring to obtain a solution B; and adding the solution B into the mixture A, performing uniformstirring, pouring the stirred solution into a mold, performing compression moulding to obtain a perlite heat preservation board blank body, performing primary drying, performing secondary drying, andperforming tertiary drying to obtain the perlite heat preservation board. The perlite heat preservation board provided by the invention has good heat preservation performance, high compressive strength, is not easy to damage, and has high durability.