The invention relates to the field of botany and pesticides and particularly relates to a pharmaceutical composition for prolonging blooming period of plants and a preparation method therefor. The pharmaceutical composition disclosed by the invention is prepared from Ilex cornuta, hollyhock roots, ilex latifolia, radix glycyrrhizae, chive seeds, diammonium phosphate and potassium sulfate. Proven by blooming period regulation and control tests, the pharmaceutical composition disclosed by the invention can be used for effectively prolonging the blooming period of the plants; through a formula of combining natural medicinal plants and commonly-used phosphate fertilizers and potash fertilizers, the pharmaceutical composition disclosed by the invention achieves a more outstanding blooming period prolonging effect compared with that using the phosphate fertilizers and potash fertilizers independently; and the pharmaceutical composition is simple in formula, easy in quality control, convenient in use and good in safety.