Fieldbus is a digital network applied in process control field, it contains not only the process control information exchange, but also contains the equipment management information communication. Through field bus, all kinds of smart devices (smart transducer, adjusting method, analyzer, and distributed I/O units) can be easily exchanged for data and process control strategy can be fully realized in the site equipment level. At present, the fieldbus that has been mostly used mainly is the FUNDATION fieldbus (FF bus) and the Profibus fieldbus. Application of fieldbus technology can conveniently connect the smart devices and I/O units distributed at site, to consitute a control system. This structure has already become the trend of development DCS.