The invention belongs to the biopharmaceutical. It involves the role and mechanism of PCSK9 in inflammatory immune diseases, and the application of PCSK9 inhibitors to the preparation of drugs for the treatment of inflammatory immune diseases mediated by T cells. In particular, it involves the use of PCSK9 monoclonal antibody, PCSK9 interference RNA and PCSK9 small molecule inhibitors for treating psoriasis, atopic dermatitis, or urticaria. The invention uses psoriasis as an embodiment for the study of inflammatory and immune diseases. It is found that PCSK9 plays an important role in the treatment of inflammatory immune diseases. The PCSK9 monoclonal antibody, PCSK9 interference RNA, and PCSK9 small molecule inhibitor can be further developed for treating inflammatory immune-diseases, such as psoriasis with fewer adverse reactions, at low cost, and with good efficacy.