The invention relates to a charcoal-based organic fertilizer and a preparation method thereof. The charcoal-based organic fertilizer has the advantages of low cost, environment friendliness, good fertilizer efficiency, wide application range, high fertilizer efficiency utilization rate and pest prevention. The preparation method comprises the steps as follows: adding starter cultures to chicken manure and soybean meal respectively for fermentation, after drying, crushing and mixing crop-residue-derived carbon, the treated chicken manure and soybean meal with ground phosphate rock, adding wood vinegar to the mixture with stirring, performing granulation, and obtaining the charcoal-based organic fertilizer after cooling and drying.