The invention relates to a high-concentration biological liquid calcium fertilizer. The high-concentration biological liquid calcium fertilizer comprises a composite probiotics agent, calcium ammoniumnitrate, and sugar alcohol, the mass parts of each component are as follows, the composite probiotics agent is 20-40 parts, the calcium ammonium nitrate is 50-70 parts, and the sugar alcohol is 5-20parts. The preparation method of the biological liquid calcium fertilizer comprises the following steps: injecting carbon dioxide exhaust gas into a heating system, adding molasses and wheat bran, heating the materials, and preserving the materials; cooling a mixture prepared as described above, adding the compound probiotic bacteria species, and sealing and stirring the materials; then transferring the materials to a fermentation cylinder through a centrifugal pump for temperature-changing fermentation, and preparing the composite probiotics agent; placing the composite probiotics agent in the fermentation cylinder, performing heating and insulation, and adding sugar alcohol and calcium ammonium nitrate and stirring the materials for storage. The fertilizer has the advantages of quick fertilizer efficiency, high absorption rate, and quick supplement of calcium element, supplys quick nutrient required for microbial activity, accelerates microbial breeding and activity, and is beneficial to the dissolution of poorly soluble nutrients in the soil. The preparation method has the advantages of short time and low cost, and the prepared liquid calcium fertilizer has high calcium contentand stable performance.