The invention relates to a PVC (Polyvinyl Chloride) microcrystalline wood composite material and a preparation method thereof. The PVC microcrystalline wood composite material provided by the invention is mainly prepared from the following raw materials: 100 parts of PVC, 10 to 80 parts of pulverized biomass, 10 to 140 parts of sulfate, 2 to 6 parts of stabilizer, 0.4 to 1.5 parts of foaming agent, 4 to 10 parts of foaming control agent, 3 to 8 parts of flexibilizer, 0.3 to 2.0 parts of lubricating agent, and 0.3 to 1.8 parts of coupling agent. The invention also comprises a preparation method of the PVC microcrystalline wood composite material. The toughness and the rigidity of the PVC microcrystalline wood composite material prepared by the method are superior to those of an existing PVC microcellular foaming wood plastic material, especially the shrinking percentage of the material is remarkably reduced, the vicat softening point temperature is remarkably improved, and the PVC microcrystalline wood composite material can be widely applied in building materials such as indoor and outdoor floors, wallboards, top plates and home furnishing.