The invention discloses an application of MBL in preparing a drug for preventing or treating disease induced by an effector T cell and belongs to the technical field of a novel application of mannan binding lectin. The key point of the technical scheme is as follows: the invention relates to the application of MBL in preparing a drug for preventing or treating infectious diseases, autoimmune diseases or/and allergic diseases induced by the effector T cell, wherein MBL realizes functions of the drug by enhancing iTreg cell and inhibiting proliferation of the effector T cell. Through researches, a novel factor of adjusting the inhibition function of the Tregs cell is obtained, that is, MBL directly enhances the inhibition action of the Tregs cell on proliferation of the effector T cell. The application disclosed by the invention highlights a novel function of MBL, and MBL not only plays an important anti-infection role in inherent immunity, but also can be a pertinent target spot for treating various autoimmune diseases and inflammatory diseases in intervention of the function of the Tregs cell.