Provided is a use of miRNA-214 inhibitor in inhibiting regulatory T cells (Treg cells). The microRNA-214 (miRNA-214) can promote Treg cells, and can assist tumors in immune escape. The experiments demonstrates that the inhibition of miRNA-214 can inhibit the growth of Treg cells, thus inhibiting the growth of tumors. Therefore, miRNA-214 can be used for developing an anti-tumour drug or a drug inhibiting immune response hyperactivity.