Background <p>Information and communication technologies (ICTs) play a significant role in maintaining cognitive function among older people. However, there is limited research on the association between Internet usage and cognitive function. This study aimed to investigate the association between diverse Internet usage patterns and cognitive function, as well as the underlying mechanisms, in Chinese older people.</p> Methods <p>We analysed data from 8,349 respondents enrolled in the 2020 China Health and Retirement Longitudinal Study (CHARLS). Ordinary Least Square (OLS) regression was performed to examine the effects of diverse Internet usage purposes and access devices on cognitive function among older people. The propensity score matching (PSM) was employed to estimate the average treatment effect of Internet usage on cognitive performance and to validate the robustness of the findings.</p> Results <p>Internet usage was significantly associated with higher cognitive scores among older people in China (β = 1.74, 95% CI 1.51–1.97). Specifically, watching news (β = 0.46, 95% CI: 0.28–0.64) and playing games (β = 0.11, 95% CI: 0.01–0.23) were positively associated with cognitive scores. Accessing the internet via desktop computers (β = 0.64, 95% CI: 0.06–1.21) and mobile phones (β = 0.32, 95% CI: 0.05–0.59) was also associated with better cognitive scores compared with non-users. Social participation partially mediated the association between Internet usage and cognitive function. The positive effects of Internet usage on cognitive function were more pronounced among urban residents, females, and those aged 71 to 80.</p> Conclusions <p>Internet usage plays a crucial role in maintaining cognitive function in older people. Targeted efforts to improve Internet access and usage, as well as enhance social participation, may significantly promote cognitive health among older people.</p>