BACnet (Building Automation and Control networks) is a standard data communication protocol for building automation and control systems. The purpose of the BACnet network layer is to provide the means by which messages can be relayed from one BACnet network to another, regardless of the BACnet data link technology in use on that network. BACnet Router is the BACnet network layer interconnect equipment, and its role is to connect BACnet networks, form BACnet Internet, and route messages between BACnet networks. In addition, establish and maintain routing tables, network congestion control is one of the main contents of the BACnet network layer. In this paper, the authors analyze the features of the BACnet network layer and the characteristics of the BACnet routers congestion control algorithms firstly, and then specify the current widespread use of congestion control algorithms, finally propose a new congestion control algorithm named IRCCA (improved router congestion control algorithm) on the basis of these present algorithms. Application of this algorithm with BACnet routers can solve the BACnet network's congestion control problem and improve the BACnet network's reliability and real-time performance.