Type 2 diabetes mellitus (T2DM) is an important risk factor of cardio-cerebral vascular disease such as coronary heart disease. GLP-1 is a kind of incretin secreted by the L-cell located in Ileum. It acts as an incretin hormone by protentiating glucose-stimulated insulin release. Recent studies reported that GLP-1 RA can protect the vascular endothelial and prevent vascular from atherosclerosis. Investigators design this study to investigate exenatide's effect on the improvement of the coronary endothelial function by evaluating endothelium dependent diastolic function and testing the vascular endothelial active substance and related inflammatory factors.

Inclusion Criteria:

• Females or males, and aged 20 to 65 years
• Newly diagnose type 2 diabetes mellitus with BMI>25kg/m2.
• HbA1C>8%.

Exclusion Criteria:

• Type 1 diabetes mellitus, diabetic ketoacidosis, diabetic hyperosmolar coma.
• Hepatic insufficiency (ALT or AST> 1.5*ULN).
• Renal insufficiency [Creatinine clearance rate (Ccr)]<60ml/min estimated from MDRD equation).
• Thyroid disease
• Use of any anti-diabetic, anti-hypertension or anti-dyslipidemia drugs.
• Pregnant or lactating woman.
• Severe anemia.
• Acute myocardial infarction or stoke.
• Other conditions at investigator's discretion.