The invention discloses a styrene-based non-halogen flame-retardant injection-grade wood-plastic composite material and a preparation method thereof. The wood-plastic composite material comprises the following components by mass percentage: 25% to 60% of styrene-based resin, 5% to 50% of vegetable fiber, 0.5% to 20% of compatibilizer, 0% to 30% of toughener, 0.5% to 8% of dispersant, 5% to 40% offlame retardant and flame-retardant synergist and 0% to 1% of antioxidant. Compared with the existing wood-plastic composite material, the styrene-based non-halogen flame-retardant injection-grade wood-plastic composite material prepared by the invention has the characteristics of simple production procedure, lower flame-retardant consumption, good non-halogen flame-retardant effect and wide range of forming manners. Therefore, the invention is suitable for various injection-molded parts, such as the housing of electrical products, furnishings, automobile materials, artworks, complex-structured building products and the like.