The study will be a 36-week multicentre, double-blind, placebo-controlled phase Ⅱb trial in China. Total 360 participants aged 55-80 years will be randomized to Tian Ma Bian Chun Zhi Gan group (84mg per day) or to placebo group. The primary endpoint will be Vascular Dementia Assessment Scale-cognitive subscale and Clinical Dementia Rating-Sum of Boxes. Secondary outcomes included changes in Mini-Mental State Examination, Clock Drawing Test, Delayed Story Recall and Ability of Daily Living. Patients' safety will be assessed by recording of adverse events, clinical examinations, electrocardiography and laboratory tests. The patients, caregivers, and investigators will be blinded to the treatment allocations.

Inclusion Criteria:

1. Concerns of a patient, knowledgeable informant or a clinician of decline from a previous level of cognitive functioning.
2. Clear and significant deficits in objective assessment in two or more cognitive domains, Memory decline, delayed story recall ≤10.5point(maximum is 56 point), or visuoconstructional-perceptual ability, clock drawing test≤3point(maximum is 4 point);or executive function, trail making test-part B≥188.5 second( maximun is 300 second); or language function, boston naming test-30 items ≤21.5 point( maximum is 30);
3. Global cognitive impairment, mild to moderate dementia with Mini-mental state examination(MMSE) score of ≤26 and ≥11;
4. Cognitive deficits are severe enough to impair social or occupational functioning, the ability of daily living scale ≥16 points;
5. Determining evidence of significant cerebrovascular disease, presence of significant neuroimaging (MRI or CT) evidence of cerebrovascular disease (one of the following): a) multiple (≥2) large vessel infarcts ; b) Single lacunes placed strategically in the thalamus or basal ganglia; c) Multiple lacunar infarcts (≥3) outside the brainstem; d) 1-2 lacunes may be sufficient if strategically placed or in combination with extensive white matter lesions; e) extensive and confluent white matter lesions; f) watershed infarction with moderate white matter lesions; g) Strategically placed intracerebral hemorrhage, or two or more intracerebral hemorrhages; h) combination of the above.
6. A relationship between dementia and cerebro-vascular disease, manifested or inferred by the presence of one or more of the following: a) abrupt deterioration in cognitive functions, the onset of the cognitive deficits is temporally related to one or more cerebro-vascular events , onset of cognitive deficits within 3 months following a recognized stroke, and cognitive deficits persisting beyond three months after the event, and abrupt with a stepwise or fluctuating course owing to multiple such events; b) gradual onset and slowly progressive course, evidence for decline is prominent in speed of information processing, complex attention and/or frontal-executive functioning in the absence of history of a stroke or transient ischemic attack. One of the following features is additionally present: ①Early presence of a gait disturbance; ②Early urinary frequency, urgency, and other urinary symptoms not explained by urologic disease; ③Personality and mood changes: abulia, depression, or emotional incontinence
7. Aged ≥55 and ≤80 years old in both gender;
8. Weighing of ≥45kg and ≤90kg;
9. Adequate vision and hearing ability to complete all study tests;
10. With a stable caregiver.
11. Informed consent, signed informed consent by legal guardian.

Exclusion Criteria:

1. Have cognitive impairment caused by other types of dementia, mix dementia, Alzheimer's disease(Medial temporal atrophy scale (MTA) score is ≥1.5 (adjusted by age: 65-74 years ≥ 1.5, 75-84 years ≥ 2.0) at baseline MRI screening),frontotemporal dementia, Parkinson's disease dementia, Lewy body dementia, Huntington's disease, etc;
2. Subdural hematoma, traffic hydrocephalus, brain tumor, thyroid disease,vitamin deficiency or other diseases which can lead to cognitive impediment;
3. mood disorders, like depression disorder (HAMD≥17) or anxiety disorder (HAMA≥12);
4. Subject can't complete related test due to severe neurologic deficits, such as hemiplegia, aphasia, audio-visual disorder and so forth;
5. Severe cardiovascular disease(severe arrhythmia, myocardial infarction within 3 months, New York Heart Association Functional Classification III-IV, systolic pressure≥180mmHg or ≤90mmHg);
6. Severe liver or kidney dysfunction, alanine aminotransferase or aspartate transaminase is more than 1.5 times the upper limit of normal, or serum creatinine is more than the upper limit of normal;
7. Uncontrolled diabetes(glycosylated hemoglobin is more than 10%);
8. Asthma, chronic obstructive pulmonary disease, multiple neuritis, myasthenia gravis and muscle atrophy;
9. Severe indigestion, gastrointestinal obstruction, gastric and duodenal ulcers and other gastrointestinal disorders that can affect drug absorption;
10. A medical history of epileptic history, glaucoma, alcoholism, or psycho-substance abuse;
11. History of taking cholinesterase inhibitors, memantine, or proprietary Chinese medicines with clear nootropic effects for the last 1 month;
12. Have taken medications (e.g., antidepressants, benzodiazepines) that affect the central nervous system (CNS), except those for AD, less than 4 weeks；
13. History of hypersensitivity to the treatment drugs;
14. Participate in other clinical study for the last 1 month;
15. Have metal (ferromagnetic) implants, or a cardiac pacemaker and other conditions that make MRI scan not applicable;
16. Or any other conditions that, in the investigator's opinion, could interfere with the analyses of safety and efficacy in this study.