Abstract: As a new type of vehicle for urban air transportation, UAS entering the urban airspace will bring huge security risks to ground public safety. This paper summarizes the current research status of domestic and foreign scholars on UAS operation ground risk assessment and UAS operation planning from three aspects: analysis of risk elements of UAS operation, urban area risk distribution map and route planning method based on risk map. Finally, the research trend of UAS operation planning based on acceptable risk in urban airspace is prospected. It is pointed out that considering fine UAV risk operation mode will be a focus and trend of urban air traffic management research in the future.