The invention provides a pesticide water solution and a preparing method and application thereof. The pesticide water solution comprises the following raw materials: 0.1-20% of amino-oligosaccharin, 0.1-20% of tetramycin, 1.0-10% of a wetting dispersant, 1.0-10% of penetrant, 3.0-8.0% of an antifreezing agent, 0.1-5% of an antifoaming agent and the rest of water. The ingredients are uniformly mixed into a transparent brown according to the requirements of a formula, thereby obtaining the pesticide water solution. The biological pesticide amino-oligosaccharin is used as the signal molecule (elicitor) of the pesticide water solution, a plant is rapidly and effectively induced to produce defense reaction, the SAR (System Acquired Resistance) of the plant is activated, and a broad spectrum effect of preventing and treating bacteria and fungi is realized through the combination of the biological pesticide tetramycin. The amino-oligosaccharin and the tetramycin are scientifically compounded so as to increase the effect of each other in a synergistic way. The pesticide water solution has the advantages of rapid effect taking, long lasting period, broad sterilizing spectra, no toxicity, no residue and the like. The preparing method is simple, has a wide range of applications and is suitable for the requirements of large-scale industrial production.