The invention relates to a preparation method and the application of a biochar-based conditioner for cadmium contaminated soil. The preparation method comprises the following steps: firstly, mixing biologic materials with sludge, or separately using the sludge and adjusting the moisture content to 10 to 90 percent; adding calcareous materials, carrying out high-temperature carbonization in the oxygendeficit or oxygen-free environment to obtain calcium-loaded biochar; secondly, adding a zeolite powder into a soluble phosphorus solution, carrying out soaking treatment, standing and carrying outair drying to obtain phosphorus modified zeolite; thirdly, uniformly mixing the calcium-loaded biochar obtained in the first step with the phosphorus modified zeolite obtained in the second step according to the ratio of 2-5 to 1, moisturizing, aging and drying, so as to obtain a finished product. The preparation method disclosed by the invention has the advantages of simple technology, low energyconsumption and no pollution discharge in the processing process. The biochar-based conditioner for the cadmium contaminated soil is mixed with the soil for use according to a certain proportion, sothat the absorption of plants to heavy metal cadmium can be reduced by 30 to 50 percent.