There is accumulating evidence that smoking increased the risk of dementia in the elderly, studies on the relationship between passive smoking and cognitive impairment or senile dementia has been done recently. There is few studies focusing on the role of secondhand smoking on developing dementia and controversy still exists. This paper provides epidemiological basis for movement of tobacco control and prevention of senile dementia by studying the related literature at home and abroad, summarizing passive smoking exposure assessment and senile dementia screening and diagnosis method, and sorting out the relationship between passive smoking and cognitive impairment or senile dementia.