The invention provides a formula for preparing ultra-light high-elasticity fire-resistant water-resistant paper pulp foam by adopting a wood fiber raw material and a preparation method of the paper pulp foam. The paper pulp foam is composed of the following components, in parts by weight: 100 parts by weight of the pulverized natural wood fiber raw material, 0.5-10 parts by weight of a fireproof crosslinking auxiliary agent, 0-20 parts by weight of chitosan, 0.5-10 parts by weight of a foaming agent, and a plurality of parts by weight of water, wherein the natural wood fiber raw material has aweight fraction of 0.5-2% by weight in water. According to the method provided by the invention, the natural wood fibers are used as the raw materials and uniformly distributed into a solution containing the fireproof crosslinking auxiliary agent, an appropriate amount of chitosan solution is added, the foaming agent is used to promote foaming, finally dry molding is performed in vacuum or an oven, and therefore the fireproof paper pulp foam having good mechanical properties is prepared; the raw materials used in the preparation process have low costs, and the method is green and environmentally friendly, has low energy consumption in the technological process, and is suitable for large-scale production; and the prepared paper pulp foam has excellent performance and broad market prospects.