The invention relates to the field of aquaculture, in particular to a degradation ingredient for leech culture. The degradation ingredient is prepared from, by weight, 120-140 parts of protein nutrient solution, 22-24 parts of photosynthetic bacteria, 20-22 parts of lactic acid bacteria, 18-20 parts of actinomyces, 15-17 parts of yeast, 13-15 parts of fermentation filamentous bacteria, 10-12 parsof vitamins, 8-10 parts of trace elements and 7-9 parts of sugar. By utilizing beneficial substances in microbial flora for mutually symbiotic multiplication, residual baits and waste in the water aredecomposed, silt at the water bottom is reduced, oxygen is increased, and the water quality is improved; meanwhile, spoilage bacteria are inhibited, the body balance of aquatic animals is maintained,the immunity is improved, and the death is reduced; the PH value of the water body is stabilized, the trace elements are supplemented, and harmful substances in the water are removed through the utilization of beneficial flora; the proportion relationship between the beneficial flora and plankton of the water body is balanced; breeding and growth of harmful algae are inhibited; amino nitrogen andnitroso nitrogen in the water are quickly and thoroughly degraded by using the flora, harmful substances such as hydrogen sulfide are eliminated, the quality of aquatic products is improved at the same time, and the aquatic products develop in the green and pollution-free direction.