The present invention discloses a water-retention fertilizer special for tobaccos and used for preventing and controlling Ralstonia solanacearum. The fertilizer comprises the following raw materials: maize straws, yeast residue, seaweed residue, cruciferae plants, Auricuralia auricular fermented bran, urea, ammonium dihydrogen phosphate, potassium chloride, manganese sulfate, EDTA-chelated magnesium, EDTA-chelated iron, phosphomolybdic acid, borax, EDTA-chelated calcium, calcium beta-methyl-beta-hydroxybutyrate, sodium silicate, calcium carbonate, phosphorous acid, benzothiadiazole, beta-aminobutyric acid, black mica, quartz, potassium feldspar, chitosan, bacillus, salicylic acid, jasmonic acid methyl ester, vanillin and a water-retaining agent. The prepared water-retention fertilizer special for tobaccos and used for preventing and controlling Ralstonia solanacearum is reasonable in formula, comprehensive in nutrition, and good in water retention effect. Meanwhile, the growth of tobaccos is facilitated. Both the drought resistance and the disease resistance of tobaccos are improved. The occurrence of Ralstonia solanacearum is effectively prevented. Meanwhile, the quality of tobaccos is improved.