The invention discloses a preparation method of a wood-ceramic composite material, and belongs to the technical field of building materials. The preparation method comprises the following steps: firstly cutting woods into boards, and then carrying out heating treatment on the boards in a nitrogen-protection state to obtain pretreated boards; carrying out enzymolysis on the pretreated boards to manufacture dried and enzymolyzed boards, then dipping in saturated solution with sodium sulfate and urea, after cooling and crystallizing, taking out, draining water, drying till the weight is constant,thus obtaining dried and dipped boards, carrying out pressure-maintaining treatment on the dried and dipped boards in a high-pressure kettle by using nitrogen containing trimethylaluminum, manufacturing a board blank, finally heating and pyrolyzing the board blank in the nitrogen-protection state, cooling and discharging to obtain the wood-ceramic composite material. The wood-ceramic composite material prepared by the invention has excellent mechanical property and flame retardance.