Diabetes has become important risk factors for threatening human life and health. Studies have shown that chronic hyperglycemia lead to microvascular brain injury. The more common types of dementia are Alzheimer's disease (AD). Cognitive dysfunction is a precursor to Alzheimer's disease. Mild cognitive impairment (MCI) is a cognitive impairment between normal aging and dementia, mainly manifested as memory impairment, especially episode memory defects, but also named obstacles, but the overall cognitive function is normal, daily life ability is normal. Studies have shown that middle-aged diabetic patients' cognitive ability will decline by about 19% in 20 years compared to people without diabetes.

Sulfur amino acid is the indispensable amino acid in mammals, and its metabolites include Taurine, Hydrogen sulfide (H2S) and sulfur dioxide (SO2). Taurine was first isolated more than 150 years ago from ox (Taurus) bile. Although the taurine can be synthesized in vivo by cysteine in the presence of cysteine dioxygenase, it is mainly acquired from dietary sources, such as eggs, meat, and seafood. H2S is a biologically relevant mediator and plays potential roles in several physiological processes and disease states in the body. H2S is synthesized from 2 sulfur-containing amino acids, l-cysteine andl-methionine, by the 3 enzymes,cystathionine-γ-lyase (CSE), cystathionine-β-synthetase(CBS), and3-mercaptopyruvate sulfurtransferase (3-MST). Previous studies have demonstrated that Taurine and H2S may play important roles in the development of themicroangiopathy and lower extremity arterial occlusive.

Inclusion Criteria:

• Type 2 diabetes

Exclusion Criteria:

• Type2 diabetes with acute diabetic complications.
• Type1 diabetes.
• History of depression, schizophrenia or dementia.
• History of cardio-cerebral vascular events, such as congestive heart failure, myocardial infarction or stroke within 3 months.
• History of parkinson's diseases, head injury,toxic encephacopathy,epilepsy.
• Hypohepatia (AST or AST is twice higher than the upper limit) or history of hepatitis or cirrhosis, hepatic encephalopathy.
• Renal insufficiency (serum creatinine 1.5 times higher than the upper limit) or history of dialysis and nephritic syndrome.
• Acute infections, tumor, severe arrhythmia, mental disorders, alcohol or medicine addiction.
• Fertile woman without contraceptives.
• Any surgical or medical conditions that significantly influence absorption, distribution, metabolism or excretion of the intervention drugs.
• Allergic to or have contraindication to the intervention drugs.