Although the cloud computing has more and more extensiveapplications,it is hindered by problems such as non-support of high mobility or geographical position information,high latencyand so on.To this end,fog computing has emerged,where cloud computing is extended to the edge of the network to decrease the latency and network congestion.This paper first introduces the concept,characteristics,and a reference architecture for fog computing,then discusses the application scenarios and the issue of fog computing security.Similar paradigmsto fog computing like in-situ computing and edge computing are also delineated.Finally,the distinctions and relations between cloud computing and fog calculation are given,and the future development direction of the fog is analyzed.Fog brings computing from the core tothe edge of the network,which expands the network computing paradigm characterized by cloud computing,thus will be applied to more and more extensive serviceforms and types.