The invention relates to the field of soil improving agents, in particular to a preparation method of a compound biological fertilizer for soil controlling. The preparation method has the advantages that the waste biomass is prepared into charcoal, the charcoal is modified, and the surface contains carboxyl and other function groups, so that the stronger ion exchange ability is realized, and the pollutants in soil can be adsorbed; the nitrogen fixing, phosphor decomposing and potassium decomposing strains are separated from the garden soil, the nitrogen-fixing bacteria are used for fixing nitrogen and excreting auxin, the phosphor decomposing and potassium decomposing bacteria are used for converting invalid potassium and invalid phosphor in the soil into quick-acting potassium and quick-acting phosphor, the multiple elements of silicon, manganese, zinc, molybdenum and the like in the soil can be released out, and the nutrition level is improved; the phosphor decomposing and potassiumdecomposing bacteria are used for producing gibberellin, cytokinin, indoleacetic acid and other matters in life activity, and the plant growth is promoted; by mixing organic and inorganic fertilizers,the effectivity of nutrients in the fertilizer is improved, and the soil quality is improved; by adding an adhesive, the mixed fertilizer is wrapped, the fertilizer with slow release effect is formed, the decomposing is easy, the fertility time is prolonged, and the utilization rate of the fertilizer is improved.