Abstract: Cyber-Physical System (CPS) has become a hot research area, because it is an emerging trend around the world for fundamental technological and economic forces. Event is a key element who transforms the physical data into the semantic model. The complex events in CPS have following characteristics: interactivity and dynamic feedback, context correlation, streaming events and the uncertainties in event composition rules which bring challenges to research. In this study, the notion, characteristics and research significance of the event in CPS are represented firstly. Then, the research development of event processing techniques of the CPS and its related research fields are summarized. Finally, as the most important part, the challenges to be dealt with for event processing in CPS and the future research contents are discussed.