Based on social cognitive theory and knowledge co-creation theory, this study constructs a model of the influencing factors of group knowledge co-creation behavior among users in online health communities. Using questionnaire data, the structural equation model is used to empirically analyze the impact and mechanism of user self-efficacy, community environment, and health information on group knowledge co-creation behavior. The results show that both user self-efficacy and health information significantly and positively promote group knowledge co-creation behavior; the direct impact of community environment on group knowledge co-creation behavior is not significant, but it shows a significant total effect through the mediating effect of self-efficacy and health information; self-efficacy significantly and positively affects the acquisition and utilization of community environment and health information, verifying the applicability of the social cognitive theory and the knowledge co-creation theory in the study of group behavior in online health communities. Therefore, online health communities should focus on the capacity building and motivation of user groups to enhance their self-efficacy, strengthen the quality control and authority of health information to provide a reliable basis for reaching group consensus, and optimize the design of the community environment to guide user groups to shift from information reception to active co-creation.