The automatic control system of water and liquid fertilizer mixed irrigation, combination of open and closed loop, has been developed successfully based on wireless sensor network. In the closed-loop part of the system, the information of each greenhouse soil moisture is collected by end nodes and sended to coordination node after routing relay, the coordinator control water irrigation automatically depended on the information received. In the open-loop part of the system, the user instructions and the information of target tents, irrigation volume, the ratio of biogas liquid and water, etc. are received, then the system intermixes water and liquid fertilizer and conveys mixed liquor to target tents according to the instruction and the information automatically. The closed-loop part and the open-loop part of the system seamlessly integrate, and each part of the system can also work independently, and the system disperse business logic function to different nodes to realize distributed control. In addition to this, the system effectively improves the utilization of water and fertilizer and its cost is low, and has the high promotion and application value.