Ecological momentary assessment （ EMA ） is not a single research methods, but a paradigm. It emphasizes the real-time data collection and repeated assessment of the real world, and illustrates the relationship between the natural exist and change in variables. It has high ecological validity. The use of EMA can enhance our understanding of the active interaction between individuals and environment. The basic design idea of EMA includes Event-Based Designs 、Time-Based Designs and Combination Designs. In the use of EMA , researchers also need to pay attention to some problems such as the development of software and hardware , ethical problem ,and the data problem. At present, EMA is most widely applied in clinical psychology and behavior studies.