The invention discloses a biomass carbon base fertilizer for improving acidic soil and preventing and treating tobacco root and stem diseases. The biomass carbon base fertilizer consists of the following three materials in percentage by weight: 60-80 percent of peanut shell carbon with 80-100-mesh granularity, 5-20 percent of wood vinegar concentrate and 5-25 percent of potassium humate. The preparation method comprises the following steps: mixing the three materials together, uniformly stirring, packaging and storing in separate bags according to the needed weight. The biomass carbon base fertilizer disclosed by the invention has the advantages that 1, the problem that the peanut shells cannot be reutilized is solved, wastes are changed into valuable materials, and the influence of the environmental pollution is reduced; 2, the production process is simple, environment-friendly side effects are avoided, the products are all natural, and the additional value is high; and 3, the product is environment-friendly and safe. The matrix materials used for the fertilizer are natural materials and are easily degraded after being applied to soil, the utilization rate is high, and residues are avoided. The biomass carbon base fertilizer is a novel environment-friendly functional organic fertilizer.