This study takes HPV vaccine promotion on Chinese social media platforms (taking WeChat as a case) as the research focus. Grounded in Van Leeuwen’s theoretical framework of “discourse as the recontextualization of social practice” and O’Halloran’s multimodal recontextualization analytical model, it systematically compares multimodal strategies between an official medical guideline and a popular WeChat article in health communication. The study demonstrates that multimodal resources significantly shape public risk perception and behavioral motivation: WeChat posts enhance the accessibility and persuasiveness of health information by reducing cognitive load (e.g., simplified representation of vaccine mechanism), evoking emotional resonance (e.g., vivid illustrations of young female patients), and increasing legitimation via personifying viruses. Through the analysis, the findings reveal that official documents construct scientific authority through professional terminology, data tables, and hierarchical layouts, whereas WeChat articles employ visual metaphors (e.g., anthropomorphic virus imagery), emotional narratives, and interactive designs to reconstruct the social practice of vaccination. On the above basis, this research not only highlights the potential of multimodal discourse in digital public health interventions but also provides methodological insights for increasing public acceptance in health communication. Future studies could investigate audience’s acceptance or cross-cultural comparisons, exploring in-depth understanding of the communicative power of multimodal public health discourse.