[Objective] This paper reviews the literature of the online health research, and discusses their methods, hot topics, theme evolution, and trends, aiming to provide reference for exploration in the future. [Coverage] The data are selected from Web of Science core collection by using the keywords of "Online medical" or "Online health", finally 1,899 English articles were retrieved. [Methods] This paper mainly relies on the methods of bibliometrics, cluster analysis and vertical mapping analysis. [Results] Internet medical and health information, social media, online health community, electronic health records are the hot topics which are influenced by the diversification of Internet information and the convenience of online communication. [Limitations] This paper does not retrieve data from other databases and analyze the full text. The results might be biased. [Conclusions] There are still much to be explored in the field of online health. Combined with image recognition, deep learning and neural networks, more researches can be conducted in the future.