The purpose of this study is to reveal the relationship between users' online health information search and perceived health risk bias, to enrich the research results of cognitive bias in the field of information behavior, and to provide suggestions for comprehensively improving people's health cognition level. Based on the existing research foundation, relevant hypotheses were put forward, and the OLS model, the instrument variable method and the moderating effect model were used to test the relationship between users' online health information search and health risk perception bias using CGSS2021 data.The results show that the frequency of  online health information search has a significant negative impact on health risk cognitive bias, and the moderating effect of online health information topic search intensity and online health information search outcome is significant. The results of this paper can provide a reference for exploring the mechanism of health risk cognitive bias in online health information search, and have important practical significance for giving full play to the advantages of online health information search and reducing users' health risk cognitive bias.