Alzheimer's disease (AD) is the commonest cause of dementia. There is no effective treatment to cure the disease. Cholinesterase inhibitors, such as donepezil, are widely recommended to patients with mild to moderate AD. But the cognitive function of most of the patients using donepezil gradually aggravate, with Mini-Mental State Examination(MMSE) score falling by 2 points per year on average, and donepezil cannot effectively delay AD progress.