In this paper, we propose a communication method with IP-based wide area networks for SCADA systems. This method controls communications between substations and a control center and can be implemented as a communication middleware. The method supports functions for UDP-based transmission, route control of double route transmission, retransmission control and priority control. The functions work cooperatively to assure reliable and real-time communications. We also examined the effectiveness of the method under circumstances where there are not only transmission delay and route breakdown in network but also information congestion in computer. The results show that the proposed method is more effective for assuring real-time and resilient feature than TCP-based communication method.