Objective: To explore the characteristics of online health information seeking behavior among diabetic patients, identify its influencing factors, and reveal the underlying mechanisms, thereby providing a theoretical basis for optimizing health information service platforms and enhancing patients’ information literacy. Methods: A mixed-methods research design was employed. First, qualitative analysis through in-depth interviews (n = 15) was conducted to examine diabetic patients’ online information-seeking processes, exploring how antecedent factors such as information overload and perceived risk influence patients’ information-seeking behavior through the mediating role of health anxiety. Second, through literature analysis and theoretical derivation, an integrated model of online health information-seeking behavior among diabetic patients was constructed based on the CAC (Cognitive-Affective-Behavioral) theoretical framework. Results: The study identified four key characteristics of patients’ online information-seeking: (1) Information-seeking is multifaceted and progressive, evolving from symptom recognition to disease management needs; (2) Patients commonly face information overload dilemmas, struggling to distinguish information authenticity and quality, with significant advertising interference; (3) Perceived risks (medical pitfalls, privacy breaches) and information overload mutually reinforce each other, triggering health anxiety; (4) Health anxiety simultaneously drives active information-seeking and leads to over-reliance and decision difficulties. The proposed integrated model indicates that information environment quality, patient information literacy, and platform design are three critical factors influencing information-seeking efficacy. Conclusion: The transition of patients from passive recipients of medical guidance to active self-managers is an important global health trend; however, this transition faces structural barriers. Optimizing the online health information ecosystem, enhancing patient information literacy, and establishing information credibility assessment mechanisms are important pathways to improve patients’ information-seeking efficacy.