Background <p>As population aging progresses, chronic multimorbidity has become a global public health issue to affect quality of life in older adults. However, the association between internet usage and chronic multimorbidity are still uncertain. This study aims to analyze the association between the chronic multimorbidity and internet usage among middle-aged and older adults.</p> Methods <p>We used data from two waves (2018, 2020 surveys) of the China Health and Retirement Longitudinal Study. 6,955 participants aged 45 years and older were included. Chronic multimorbidity was assessed based on 15 non-communicable chronic diseases. Internet usage included internet use, diversity of internet use devices, and diversity of internet use purpose. We employed generalized estimating equations to analyze the association between internet usage and chronic multimorbidity.</p> Results <p>In the fully adjusted model, internet use, diversity of internet use devices, and diversity of internet use purposes were all significantly associated with a lower risk of chronic multimorbidity. Sensitivity analyses confirmed the robustness of these results after excluding participants with severe disability or those not included at baseline. Subgroup analyses showed relatively stronger effects among females, rural residents, and non-drinkers.</p> Conclusion <p>This study suggests that greater internet use, along with higher diversity in devices and purposes, is associated with a lower risk of chronic multimorbidity among middle-aged and older adults. Promoting digital literacy, access to devices, and online health resources may help reduce multimorbidity and enhance well-being in this population.</p>