The invention discloses a building decoration material and a preparation method thereof. The building decoration material comprises the following raw materials in percentage: 65-80% of wastes, 20-30% of plastics, 5-10% of fibers and 0-10% of additives. The preparation method comprises the following steps: firstly, preparing waste powder; secondly, smashing the plastics to obtain plastic powder, mixing the plastic powder with the waste powder, and uniformly stirring the mixture; and thirdly, adding the fibers and the additives, uniformly stirring the mixture, and then, carrying out granulation and extrusion molding to obtain a finished product of the material, wherein the wastes are mixtures of polished tile wastes, wood wastes and marble wastes or mixtures of quartz sand and stone powder. The invention provides the building decoration material and the preparation method thereof, the preparation method is simple in process and reasonable in design; and the finished product prepared by mixing the polished tile wastes, the wood wastes, the marble wastes, the plastics and the additives according to a certain ratio and carrying out extrusion molding is high in strength, bending-resistant, suitable for the field of building decoration and capable of realizing the reutilization of decoration wastes.