This study aims to evaluate the efficacy and safety of DBPR108 tablets in combination with metformin hydrochloride in the treatment of type 2 diabetes mellitus. A total of 210 subjects will be randomly assigned in a ratio of 2:1 to receive metformin hydrochloride plus DBPR108 or metformin hydrochloride plus placebo.

Inclusion Criteria:

• Diagnosis of type 2 diabetes according to World Health Organization (1999) diabetes diagnosis standard;
• Age 18-75 years, men and women;
• BMI 19-35 kg/m2;
• HbA1c 7.0%-9.5%;
• Before screening, a stable Metformin dose（≥1000mg/day）should be maintained for at least 8 weeks.
• Signed informed consent from the patient;
• Agree to use contraceptive measures from the date of signing the informed consent to 1 month after the end of the last medication.

Exclusion Criteria:

• FPG > 13.9 mmol/L;
• Insulin treatment required in the investigator's opinion;
• Administration of antidiabetic drugs (except for metformin) including insulin, rosiglitazone, pioglitazone, DPP-4 inhibitor, Glucagon like peptide-1 (GLP-1) receptor agonist for 8 weeks before screening;
• Acute complications of diabetes (including diabetic ketosis and ketoacidosis, hyperosmotic nonketotic diabetic coma, lactic acidosis and hypoglycemia coma);
• Severe hypoglycemia;
• Serious diabetic complications (such as diabetic foot, etc.);
• History of acute or chronic pancreatitis, or related diseases that are most common cause of acute pancreatitis (such as recurrent cholelithiasis, etc.);
• History of being allergic to DPP-4 inhibitors;
• Untreated hyperthyroidism and other diseases which may cause secondary hyperglycemia;
• Previous treatment with glucocorticoids (except for external use and inhalation) within 4 weeks before screening or may be used for more than 14 consecutive days during the study;
• Inflammatory bowel disease, partial intestinal obstruction or chronic bowel disease related to obvious digestive and absorption disorders;
• Aspartate aminotransferase (AST) or Alanine aminotransferase (ALT) > 3*upper limit of normal (ULN), or total bilirubin > 1.5ULN;
• Abnormal renal function;
• White blood cells (WBC) < 3.0109/l, neutrophil count of peripheral blood < 1.5109/l, hemoglobin < 100g / L, triglyceride > 5.7 mmol/l;
• HBsAg, HBeAg or HBcAb positive, or any one of hepatitis C antibody, anti-HIV antibody and nonspecific antibody of Treponema pallidum positive;
• Pregnant or lactating women;
• History of alcohol or drug abuse;
• Participation in other clinical trials or administration of any other investigational drugs or devices within 3 months before screening;
• Significant unstable diseases;
• Any condition that in the investigator's opinion might render the patient unable to participate the trial.