The communication of health knowledge in social media plays an important role in public health literacy and health behavior promotion. But with the accumulation of user-generated health knowledge in social media, more and more misleading health information, health gossip and health rumors are inhibiting the communication of health knowledge and the development of information ecology in social media. This study focuses on the information ecology in social media and contributes to the communication of health knowledge in social media ecology, highlighting the characteristics of health knowledge and the special Chinese culture. Based on the definition of three effective communication forms embedded in the communication of health knowledge—the fear communication, the trust communication and the face communication, an explanatory framework is constructed to examine their interactions and impacts on the communication of health knowledge in social media. Data collected from 329 respondents was tested using a partial-least-squares (PLS) approach. The results indicate that fear communication and trust communication both act as effective communication forms contributing to the communication of health knowledge; face communication acts as a barrier constraining the trust communication while no effect on fear communication. Theoretical and practical contributions are discussed in this paper.