Objective To explore the level of cognitive function in Chinese older adults, to explore the impact of physical activity intensity on cognitive function, and to provide references for improving cognitive function among the elderly in China and formulating preventive measures. Methods The 2020 China Health and Retirement Longitudinal Study database was searched to collect cognitive function and physical activity among older adults. Univariate and multivariate analyses were performed to identify factors affecting cognitive dysfunction in older adults. Cognitive function of older adults was stratified according to their educational level for hierarchical linear regression. Results A total of 8 162 older adults were included and their cognitive function score was (17.56±6.99), with the detection rate of cognitive dysfunction being 38.89%. The results of logistic regression showed that advanced age, female, living in rural area, night time sleep duration≥8 h, without social activities, and high-intensity physical activity were risk factors of cognitive dysfunction (all P<0.05). The results of hierarchical linear regression showed that moderate-intensity physical activity was more conducive to cognitive function than high-intensity physical activity (all P<0.05). Conclusion The incidence of cognitive dysfunction in older adults is relatively high, and the influencing factors are complex. Moderate-intensity physical activity per week is a protective factor for cognitive dysfunction among older adults.