The invention specifically relates to a culture medium prescription for cultivating immature embryo of double-petal paeonia lactiflora and a method for cultivating the seedlings of the paeonia lactiflora by using the culture medium. The culture medium comprises adventitious bud induction culture medium, adventitious bud strengthening culture medium and rooting culture medium; and the culture medium is formed by adding TDZ, cane sugar and agar based on improved MS or 1/2 improved MS. The culture method comprises the following steps: selecting the seedling embryo; preparing the culture medium; and inoculating to cultivate, wherein the step of inoculating to cultivate is the step of adopting the three culture mediums to induce the adventitious bud, strengthen the adventitious bud and root. Because of the invention, the seedling rate of the immature embryo reaches over 60%, and the technical obstacle that the double-petal paeonia lactiflora cannot establish the seedlings caused by the dysplasia of the seedling embryo. Each germination seedling embryo can establish 3-8 adventitious buds and 5-10 fleshy roots, so the effect that the seedlings of the normal seed differentiate the buds after three years is realized, the growth speed of the seedlings of the paeonia lactiflora is improved, the hybrid seedlings of the paeonia lactiflora flowers at early stage, and the breeding period of the paeonia lactiflora is shortened.