Abstract: Safety assessment in clinical trials is dependent on an in-depth analysis of the adverse events to a great extent. However, there are difficulties in summary classification, data management and statistical analysis of the adverse events because of the different expressions on the same adverse events caused by regional, linguistic, ethnic, cultural and other differences. In order to ensure the normative expressions, it's necessary to standardize the terms in recording the adverse events. MedDRA (medical dictionary for regulatory activities) has been widely recommended and applied in the world as a powerful support for the adverse events reporting in clinical trials. In this paper, the development history, applicable scope, hierarchy structure, encoding term selection and standardized query strategies of the MedDRA is introduced. Furthermore, the practical process of adverse events encoding with MedDRA is proposed. Finally, the framework of statistical analysis about adverse events is discussed.