The invention relates to a bionic filling method of the gradient of a tree body hole, which comprises the following steps: tree hole clearing: removing impurities in the tree hole; tree hole sterilizing: spraying or smearing the water solution of copper sulfate; slurry preparing: mixing an inorganic adhesive and a wood unit formed by mixing wood fiber and wood wool to prepare coarse slurry, and mixing the inorganic adhesive and a wood unit of wood powder to prepare fine slurry; slurry filling: respectively filling the coarse slurry and the fine slurry to the inner layer and the outer layer ofthe tree hole by using the central axis of the tree body as a symmetric line, and under the action of gravity, the slurry is in gradient distribution in the vertical direction of the tree hole; slurry solidifying: after the slurry is filled layer by layer, bonding the slurry with the hole wall into a whole; and simulation decorating: bonding a layer of real tree bark on the solidified filling material. Thus, the solidified filling material and the tree body filled with the filling material have the same gradient distribution rules of density and strength, thereby being more close to the flexibility of the tree body.