Detecting influencing factors on herd forwarding behavior of health information is of great implications for guiding users' rational behavior and promoting the dissemination of health information. Taking Sina Weibo platform as a case, this paper conducted three levels of coding on interview data. In open coding, 73 initial concepts and 24 basic categories were elicited. In axial coding, 8 main categories were elicited. In selective coding, herd forwarding behavior of health information was identified as the core category, and the theoretical model of influencing factors for herd forwarding behavior of health information is developed. It is found that social influence, personal preference, health literacy and perceived value have direct impacts on herd forwarding behavior of health information, while platform quality, information quality and source credibility have indirect impacts on herd forwarding behavior of health information with perceived value as the mediating factor. Finally, relevant strategies in terms of information publishing platforms, information publishers and herd information forwarders are discussed.