The invention discloses a pharmaceutical composition for preventing and/or treating allergic diseases and preparation method of the pharmaceutical composition. The pharmaceutical composition is prepared from raw materials including, by weight, 6-24 parts of astragalus, 4-20 parts of white peony root, 4-16 parts of cassia twig, 4-16 parts of fresh ginger, 4-16 parts of almond, 2-10 parts of radix sileris, 1.2-4.8 parts of cicada slough, 2.4-9.6 parts of reddish orange, 5-23 parts of jujubes (without kernels) and 4-16 parts of liquorice. The preparation method includes the steps: weighing the astragalus, the white peony root, the cassia twig, the fresh ginger, the almond, the radix sileris, the cicada slough, the reddish orange, the jujubes and the liquorice in proportion; extracting medicinal materials with water; filtering and collecting filtrate; concentrating the filtrate into extract with the relative density of 1.05-1.25 to obtain the pharmaceutical composition. The pharmaceutical composition is used for treating allergic rhinitis and allergic asthma and has the advantages of remarkable curative effect, convenience in use, rapidness in starting effects, safety, no pain and the like.