Dementia is a progressive neurodegenerative syndrome manifested by cognitive impairment, memory loss as well as behavioural and psychological disorders, which has posed a great burden on both human health and global economy. The global rising of life expectancy and an increasing proportion of elders in the population are the main reasons for worldwide population ageing (Heese, 2015).According to the World Alzheimer Report 2018, dementia affects about 50 million people and this number is expected to increase to 152 million by 2050. Among patients with dementia, 60%-98% will develop behavioural and psychological symptoms of dementia (BPSD) (Finkel, 2000). BPSD is a wide spectrum of syndromes including mood disorders, depression, agitation, psychosis, sleep disturbances, anxiety, apathy, dysphoria, aberrant motor activity, hallucinations and delusions (Lyketsos et al., 2000).The high incidence, poor prognosis, long course of the disease and serious adverse outcomes of BPSD have brought great burdens to patients with dementia and their families, particularly economic