The invention discloses a high-efficiency biogas slurry organic suspension liquid fertilizer and a preparation method thereof. The high-efficiency biogas slurry organic suspension liquid fertilizer comprises, by weight, 21.0-42.0 parts of a biogas slurry, 6.0-9.0 parts of organic matters, 4.0-25.0 parts of a nitrogen fertilizer, 9.0-20.0 parts of a potassium fertilizer, 0.5-1.0 part of a boron fertilizer, 0.5-0.8 part of EDTA-Zn, 0.4-0.6 part of EDTA-Mn, 0.1-2.0 parts of a wetting dispersant, 0.1-2.0 parts of a thickener, 0.1-2.0 parts of an antifreeze agent and 0.1-1.0 part of a root promoter. The high-efficiency biogas slurry organic suspension liquid fertilizer is an organic-inorganic suspension liquid fertilizer, and the high-efficiency biogas slurry fertilizer is prepared by fermenting a substrate biogas slurry, so the problem of the pollution of discharge of the biogas slurry to the environment is effectively solved, the biogas slurry is transformed into valuables from wastes andis fully used, and the production cost of the liquid fertilizer is reduced. The fermented biogas slurry is used to prepare the liquid fertilizer, so the liquid fertilizer can be more rapidly dissolved in water than general products, and has the advantages of high total nutrient content, stable physical and chemical properties, and no crystallization, precipitation and stratification phenomena under high temperature, low temperature and normal temperature conditions.