Abstract: From smart terminal devices such as smart phones and smart watches, to large-scale intelligent applications, such as smart homes, Internet of vehicles, intelligent life and intelligent agriculture. Artificial intelligence (AI) has gradually entered and changed the life of human being. In this context, various of intelligent devices have produced massive amount of data, making traditional cloud computing paradigm unable to adapt to the unprecedented challenge. Instead, edge computing which aims to process the data at the edge of the network has the great potential to reduce latency and bandwidth pressure, as well as protect data privacy and security. Building AI models upon edge computing architecture, training and inferring the model, realizing the intelligence of the edge are crucial to the current social. As a result, a new interdisciplinary field, edge intelligence (EI), has begun to attract widespread attention. We make a comprehensive study on EI. Specifically, firstly introduce the basic knowledge of edge computing and AI, which leads to the background, motivation and challenges of EI. Secondly, the research on EI related technologies is discussed from three aspects, namely, the problems, the models and the algorithm. Further, the typical security problems in EI are introduced. Next, the applications of EI are described from three aspects of intelligent industry, intelligent life and intelligent agriculture. Finally, we propose the direction and prospect of EI in the future development.