The present invention provides an environment-friendly plant fiber wood-plastic composite material and a preparation method thereof. The environment-friendly plant fiber wood-plastic composite material is prepared from the following components serving as base stock by weight percent: 50-90% of plant fibers, 5-40% of waste polystyrene plastic recovery particles and 5-10% of styrene butadiene styrene (SBS), as well as a proper amount of an assistant-silane coupling agent and stearic acid, wherein the use amount of the silane coupling agent accounts for 1-10wt% of the plant fibers while the use amount of the stearic acid accounts for 2-5wt% of the plant fibers. The environment-friendly plant fiber wood-plastic composite material has the advantages of insect prevention, moth resistance, chemical corrosion resistance, large additive amount of cellulose, high physical and mechanical strength, low cost, easy decomposition and wide application, and is environment-friendly.