Objective To systematacially evaluate the correlation between smoking and Alzheimer's disease（AD）. Methods PubMed，OVID， Elsevier， VIP， CNKI， WanFang and CBM databases were electronically searched to collect case-control studies and cohort studies on the association of smoking and AD. The time was from the database establishment to December 2019. Extracted data from those studies， then meta-analysis was performed with RevMan 5.3 software. Results A total of 9 case-control studies and 5 cohort studies were included. The heterogeneity of 9 case-control studies was I²=56%，P<0.05， random effect model was selected for analysis. The results were OR=0.73，95%CI：0.57-0.94，P<0.05. The heterogeneity of 5 cohort studies was I²=86%， P<0.05， and the random effect model was selected for analysis. The results were RR=0.88，95%CI：0.62-1.26，P>0.05. Conclusion Suggest that smoking exposure may be a protective factor for AD， but affected by the quantity and quality of the included literature， the above conclusions need to be verified by more high-quality studies.

Smoking, Alzheimer's disease, Meta-analysis, Case-control study, Cohort study