Abstract:The technical features of CANbus, one of the widely used fieldbus technology,is introduced in detail.the communication model as well as the Access Control Way to the communication media is analyzed.As a simple protocol CANbus has some limitations in some aspects, so according to their own features many companies developed Higher layer Protocol (HLP) based on the CAN protocol, such as DeviceNet,CANOpen,CANKingdom,SDS and so on.In this paper the features of DeviceNet protocol is introduced in detail because of its unique advantage. At the same time the characteristics and comparison of other higher layer protocol are presented.