The invention discloses a plastic wood board and a preparation method thereof. The plastic wood board is characterized by comprising the following raw materials in portion by weight: 60 to 85 portions of crop fiber, 20 to 40 portions of waste regenerated plastics, 1 to 2 portions of lubricant, 1 to 5 portions of compatilizer, and 1 to 5 portions of stabilizing agent, wherein the lubricant is paraffin, the compatilizer is one of MAPP and MAPE, and the stabilizing agent is general plastic stabilizing agent; and the raw materials are mixed, extruded, granulated, and then added with glass fiber to be pressed into the plastic wood board, and the thickness of the board is 0.5 to 40 millimeters. The plastic wood board combines the plant fiber with the waste plastics together, needs no adhesive, has no discharged pollution, can be fully recycled, has the advantages of wide application, good property, qualified single evaluation of each index, simultaneously lower requirement on equipment and no limited specification, and can be made into various specifications according to requirements of users.