The invention discloses an aquaculture water purifying agent, and relates to the technical field of aquaculture. The aquaculture water purifying agent is prepared from the following raw materials in percentage by mass : 20% to 30% of allophane, 10% to 20% of light shale powder, 8% to 10% of brucite fiber, 8% to 10% of diatomaceous earth, 8% to 10% of bentonite, 15% to 20% of coal-based activated carbon,10% to 20% of light calcium carbonate, 10% to 20% of polyaluminum chloride, 5% to 8% of thiobacillus denitrificans, 5% to 8% of bacillus licheniformis, 3% to 5% of bio-bacteria remover, 3% to 8%of corn flour, 10% to 15% of radix rehmanniae recen, 3% to 5% of flocculant, and 3% to 8% of coconut shell powder. According to the aquaculture water purifying agent provided by the invention, the allophane as a main component has the small particle size, strong adsorption capacity and is low in cost, and the prepared purifying agent is fast and effective in purification effect, high in treatmentefficiency, and small in process occupying area.