The invention discloses a flame-retarding composite material for forest fire protection and a preparation method of the flame-retarding composite material. The flame-retarding composite material comprises, by weight, 40-50 parts of a high-hydrophilic material, 40-50 parts of a high-temperature expansion material, 3-7 parts of CE(HO)4, 1-3 parts of La2O3 and 1-5 parts of Y2O3. The high-hydrophilic material is composed of one of starch and polyvinylpyrrolidone or the combination of the starch and polyvinylpyrrolidone. The high-temperature expansion material is composed of one or more of ammonium polyphosphate, dipentaerythritol and melamine. The flame-retarding material can store a large amount of water, the material can be formed into a film and cover the surface of a combustible after the water evaporates, oxygen is isolated, meanwhile, the material expands heavily in the burning process so as to separate the combustible from air, the ignition point is lowered through application of a rare earth material, and the material has excellent flame-retarding and fireproof effects for spreading of a surface-fire in the forest.