The invention relates to an application of tanshinone IIA in the preparation of medicines inhibiting keratinocyte proliferation diseases. The keratinocyte proliferation diseases comprise psoriasis, ichthyosis and keratinocyte tumors. According to the invention, a new use of the tanshinone IIA in the pharmacy is excavated, so a new application field is developed; the tanshinone IIA has a good treatment effect on skin diseases caused or characterized by the keratinocyte over-proliferation, such as the psoriasis, the ichthyosis and the keratinocyte tumors; the tanshinone IIA has been clinically used in other medicines, and a case that the tanshinone IIA has extremely small toxic side effects is proved, so the tanshinone IIA can be safely used; and the tanshinone IIA has the advantages of abundant raw material source, low price, simple preparation technology, wide industrialization prospect, and suitableness for the wide popularization and use.