The main purpose of this study is to evaluate the safety and efficacy of Huperzine A sustained release tablets in patients with mild to moderate Alzheimer's Disease.

The primary aim of this multicenter, randomized, double-blind, double-dummy, placebo- and active-controlled therapeutic trial is to determine whether treatment with huperzine A sustained-release tablets can improve cognitive function in individuals with AD.

A total of 390 participants will be randomly assigned to three groups of equal size. This will allow a comparison of huperzine A sustained-release tablets 400µg once a day, huperzine A tablets 200µg twice a day, and placebo.

The study is divided into 2 periods:

1. A two-week placebo run-in period
2. A 6-month double blind treatment period, consisting of three months of titration and three months of fixed dose treatment.

Inclusion Criteria:

1. Male/female patient aged between 50 and 85
2. Clinical diagnosis of mild to moderate probable AD based on DSM-IV and the NINCDS-ADRDA criteria
3. Middle school or above: 11 ≤MMSE ≤ 24, elementary school: 8 ≤ MMSE ≤ 20, illiteracy: 5 ≤ MMSE ≤ 16;
4. CT or MRI scan excluding another structural brain disease;
5. Hachinski Ischemic Score < 4
6. Hamilton Depression Scale ≤10
7. Informed consent of the patient (or legal representative) and of the caregiver agreeing to take part in the study.

Exclusion Criteria:

1. Proven or clinically suspected other type of dementia such as vascular dementia, mechanic or chemical caused dementia, vitamin B12 deficiency, hypothyroidism etc.
2. Epileptic Patient
3. Severe liver or renal disease
4. Resting pulse less than 50
5. Mechanical intestinal obstruction patient
6. History of stroke
7. History of angina or other severe cardiac, vascular, lung, gastrointestinal and hematopoietic system disease
8. Cognitive damage caused by alcohol or substance abuse
9. Disable to participate or cooperate in the protocol
10. Use of any agent for the treatment of dementia within 2 weeks of randomization
11. Use of another investigational agent within 3 months of screening
12. Be sensitive to Huperzine A or other ACHEIs.