The invention relates to a reagent erythrocyte preserving fluid and a preparing method thereof, and belongs to the field of medical examination. The preserving fluid comprises distilled water and sodium chloride. The preserving fluid and the method are characterized in that: the preserving fluid also comprises sodium citrate, ammonium chloride, disodium hydrogen phosphate, glucose, mannitol, adenine, chloramphenicol, sodium azide and amino acids, and the weight ratio of the distilled water, the sodium citrate, the ammonium chloride, the disodium hydrogen phosphate, the glucose, the mannitol, the adenine, the chloramphenicol, the sodium azide, the amino acids and the sodium chloride is 100 : 2-3 : 0.5-1 : 0.1-0.2 : 4-5 : 1-2 : 0.1-0.2 : 0.15-0.2 : 0.001-0.0025 : 1-2 : 2-3. By using the preserving agent for reagent erythrocyte preservation, the storage lifetime of the reagent erythrocytes is largely prolonged and can reach 90 days, thus largely facilitating fully-automatic micro-plate scan detection of reverse ABO typing for a large number of blood donors in a blood station, and carrying out of hemolytic disease of the newborn and difficult blood matching which are caused by incompatibility of blood group between the mother and fetus, and other works, and laying good foundations for serology examination and research on erythrocyte blood types.