The purpose of the trial is to verify the effectiveness and safety of glimepiride compared with sitagliptin as an add-on therapy to metformin in severe insulin deficiency diabetes.

This clinical trial is a multi-centre, prospective, intervention, randomized-controlled clinical trial, and uses a superiority test to determine whether the experimental group is superior to the control group in terms of main efficacy endpoints.

Inclusion Criteria:

• According to the World Health Organization (the WHO) 1999 criteria for the diagnosis of type 2 diabetes; the subtype was allocated to severe insulin deficiency diabetes (SIDD) at diagnosis using data-driven diabetes clusters APP.
• Men and women aged ≥ 18 years and ≤ 75 years;
• Diagnosed as severe insulin deficiency diabetes by the cluster classifier of Peking University People's Hospital at the initial stage of the disease course;
• Metformin monotherapy with dosage ≥1500 mg/day for at least 8 weeks;
• Diabetes duration less than 5 years;
• The HbA1c value of the central laboratory before randomization: 7.0% ≤ HbA1c <10.5%
• estimated estimated glomerular filtration rate (eGFR)>=60 ml/min1.73m2, alanine aminotransferase(ALT)<120U/L ;
• If other drugs are used during the course of the disease, these drugs should be withdrawn for more than 8 weeks;
• Without acute diabetic complications at present.

Exclusion Criteria:

• Type 1 diabetes or other special types of diabetes mellitus; glutamic acid decarboxylase antibody (GADA) positive, the subtype was allocated to other subtypes at diagnosis using data-driven diabetes clusters APP.
• Pregnancy or have a pregnancy plan within a year;
• Lactation or have a lactation plan within a year;
• Renal insufficiency, eGFR<60; transaminase elevated, ALT>= 120U/L; unstable coronary heart disease.
• Recurrent spontaneous diabetic ketosis or uncorrected acute diabetic complications;
• Participated in other clinical trials within 8 weeks before randomization; Unable to complete the study follow-up for 6 months; Have situations such as operation and need to change to insulin therapy in 6 months.
• Use concomitant medication such as glucocorticoids which can affect blood sugar.
• The investigator judged that it is not suitable to participate in this clinical trial.