The invention relates to a moldproof plastic-wood wallboard and a preparation method thereof. PVC (polyvinyl chloride) powder, microcrystalline calcium carbonate, wood powder, a foaming agent, foamingagent promoter, mold inhibitor, flexibilizer and polyethylene wax are adopted as materials by the moldproof plastic-wood wallboard and appropriately proportioned by weight, the PVC powder, the microcrystalline calcium carbonate, the wood powder, the flexibilizer and the polyethylene wax are first mixed and extruded to be pelletized, so that master batch is obtained, and afterwards the master batch is added with the foaming agent, the foaming agent promoter and the mold inhibitor and mixed at high speed. Thus, the PVC powder, the microcrystalline calcium carbonate, the wood powder, the flexibilizer and the polyethylene wax first undergo a pre-combining stage, the mold inhibitor, the foaming agent and the foaming agent promoter are then added and mixed at high speed, the characteristic of the promoter that effectiveness cannot be decreased due to high temperature and high shear is sufficiently exerted, ultimately the moldproof plastic-wood wallboard has a better moldproof property, andcan effectively block moisture and inhibit mold, and moreover, the moldproof plastic-wood wallboard has a good mechanical property and good toughness, and is light.