The invention belongs to the field of hydrophobic materials, and discloses a hydrophobic powder material and a preparation method thereof. Under the condition of cutting off oxygen, an unsaturated fatty acid containing at least two conjugated unsaturated bonds is used as a hydrophobic agent to combine soil with the hydrophobic agent. Mix and heat to obtain hydrophobic dispersion material. In the present invention, under the condition of isolating oxygen, the hydrophobic agent undergoes thermal polymerization reaction after heating, and the dry oil viscosity of the hydrophobic agent after anaerobic thermal polymerization is high, and it is in a semi-solid-solid state, and can be successfully attached to the surface of soil particles , forming a hydrophobic film, thereby obtaining a hydrophobic dispersion material with stable hydrophobic properties and high hydrophobic properties. In addition, the amount of hydrophobic agent used in the present invention is small, and the source is extensive, low in cost, high in cost performance, degradable, can be naturally degraded after use, and has no biological toxicity, and will not increase the content of heavy metals at the same time, and is environmentally friendly. The prospects are broad.