In view of the problems that most traditional wood preservatives are harmful to the environment and humans and animals, this paper develops a new natural biomass wood preservative with high safety, strong antibacterial ability and natural degradation. Ultrasonic extraction assisted method is used to extract tannin from Larix gmelinii, and the poplar is used as the experimental material to impregnate the poplar, and then inoculated with Coriolus versicolor and Gloeophyllum trabeum for 12 weeks. The decay resistance of wood blocks is evaluated by measuring the mass loss rate and scanning electron microscope analysis. The experimental results show that the tannin extract has a significant antiseptic effect on wood. The average weight loss rates of poplar specimens inoculated with Coriolus versicolor and Gloeophyllum trabeum are 4.36% and 15.43% respectively. Among them, when the dipping concentration of tannin extract is 5%, the treated material has the strongest inhibitory effect on Gloeophyllum trabeum. Larix gmelinii has strong antibacterial activity against wood-destroying fungi, which can effectively improve the antiseptic properties of wood.