The invention discloses a preparing method for improving the quality of blueberry bonsai. The preparing method includes the following steps that mellow soil and compound fertilizers for the blueberrybonsai are mixed to be uniform, exposure under the sun is carried out, and a bonsai medium is obtained; the bonsai medium is sent to Chinese clay pots, and water draining holes are formed in the bottoms of the Chinese clay pots; blueberries are transplanted into the Chinese clay pots containing the bonsai medium, and are watered sufficiently after planting, and the humidity of the bonsai medium reaches 42% to 50%. The compound fertilizers are prepared from, by weight, 65-78 parts of urea, 23-40 parts of ammonium sulfate, 10-20 parts of plant ash, 21-30 parts of monopotassium phosphate, 0.2-1 part of medical stone powder, 1-2 parts of fly ash, 0.4-0.8 part of calcined clay, 1-2 parts of vermiculite powder, 1-4 parts of efficient slow release formulation, 1-2 parts of hydroxyethyl cellulose,40-60 parts of organic fertilizers, 1-2 parts of honey, 0.1-0.3 part of zinc humate, 0.1-0.2 part of monoglyceride citrate, 1-2 parts of bentonite and 1-3 parts of envelope agent.