The invention relates to a water-soluble reagent for preventing pinkeye of tortoises. The water-soluble reagent comprises, by mass, 15-30 parts of plant extract, 3-5 parts of sodium chloride, 5-10 parts of vitamin A, 5-10 parts of vitamin D, 1-2 parts of lactic-acid-generating enterococcus faecium and 1-2 parts of lactic-acid-generating enterococcus faecalis. The water-soluble reagent has the advantages that a mixture of the water-soluble reagent and distilled water can have the sterilization effect, the water area environment is clear to the concentration of body fluids of the tortoises, vitamins in the bodies of the tortoises are supplemented, water quality is purified, aquatic faeces is decomposed and absorbed, and accordingly, the risk that the tortoises suffer from the pinkeye due to bacterium infection is lowered.