The invention discloses a serum or plasma miRNA marker related to diabetes mellitus type 2 and an application thereof. The invention also discloses a diagnosis kit for diabetes mellitus type 2. The marker disclosed by the invention diagnoses fat children from a microscopic view and warns the risk of long-term insulin resistance and diabetes mellitus type 2; the operation is easy, the result is accurate and objective and reliable, the diabetes mellitus type 2 group and the normal metabolism group can be perfectly distinguished, and the risk of long-term insulin resistance and diabetes mellitus type 2 of fat children can be accurately and sensitively evaluated and warned; and only a blood sample is required instead of other tissue samples, thus the possibility and feasibility of clinical application are greatly improved, and an guidance basis is provided for clinical doctors to make early prevention, intervention schemes and judgment prognosis.