Abstract: The greenhouse automatic control system is one of the key factors for increasing the profits of greenhouse production. Referring to development of industry automatic control system the greenhouse distributed automatic control system based on the fieldbus concept was developed. The system has three levels: host computer, intelligent controllers and intelligent units. The communication network between levels adopts RS-485 bus. In the software realtime database, intelligent control, opening communication protocol, realtime decision, renewed models and bidirectional watchdog were adopted. Running over a year shows that the system is reliable, perfect and recommendable to be used in greenhouse production.