The invention relates to a wood plastic plate and a preparation method thereof. The wood plastic plate is prepared from the following raw materials in parts by weight: 67 to 70 parts of modified industrial byproduct gypsum, 30 to 33 parts of waste plastic particles, 0.1 to 1 part of heat stabilizer and 0.1 to 1 part of lubricant. The wood plastic plate has the advantages that the problems of large drainage amount and low utilization rate of existing industrial byproduct gypsum are solved, the large influence of long-term stacking of the existing industrial byproduct gypsum to soil and water sources is avoided, and coal-fired power generation enterprises and chemical engineering enterprises are assisted to dispose the long-term discharged industrial byproduct gypsum.