Health misinformation dissemination on social media has caused severely negative consequences to individuals' healthcare and public health. While a large body of research on misinformation dissemination on social media exists, rare research has investigated the psychological mechanism underlying individuals' dissemination behavior. The knowledge regarding the underlying mechanism is critical not only to developing an in-depth and complete understanding of the phenomenon but also to identifying and designing effective interventions to reduce the misinformation dissemination. Anchoring on SOR paradigm and the related literature on ignorance and arousal, we develop a research model to elucidate the psychological mechanism underlying individuals' health misinformation dissemination on social media. We propose that domain knowledge deficit and emotional arousal make salient influence on dissemination behavior through credibility judgment, overestimating own ability to judge, and underestimating the negative consequences of misinformation dissemination. Research findings would make significant implications to scholars and practitioners.