The invention discloses a pharmaceutical composition for treating precocious puberty and a preparation method thereof. The pharmaceutical composition for treating precocious puberty in infants comprises the following raw materials: raw rehmannia, Alisma, Digupi, Moutan cortex, Gentiana, Prunella vulgaris, malt, turtle shell, chrysanthemum, kelp, scrophulariaceae, Gallus gallis, and oyster. The preparation method of the pharmaceutical composition comprises the following steps: S1, decocting malt for 2 to 5 times, combining the decoctions and filtering, adding an equal amount of ethanol to the filtrate, stirring the mixture and standing overnight, taking the supernatant and recovering the ethanol until free Alcoholic taste, set aside; S2, grind turtle shells and oysters into powder, put them into a cloth bag, add water to decoct with other medicinal materials for 2-5 times, combine the decoction and filter, obtain the filtrate and let it stand overnight; S3, take S2 The supernatant of the filtrate is added to the supernatant of S1 and filtered, and the pharmaceutical composition is obtained through post-processing. The invention has the effects of clearing liver and dispelling stagnation, nourishing yin and purging fire, can treat young girls' breast distension and pain and vaginal bleeding, and has the effect of treating children's precocious puberty.