Abstract：Application of BACnet/IP technology building controller, building control center via high-speed Ethernet connec原
tions in different floors，the application of different functional controller. In hardware，from the cost，performance and other
aspects identified ARM9 hardware platform，according to the system need to design the various functional modules of hard原
ware circuit；in software，embedded Linux system by transplantation，the controller provides a stable operating environment
software and network environment. This paper focuses on the completion of the use of C language realization BACnet protocol
stack，through the protocol stack，the controller with other BACnet devices for data exchange functions，proposes the appli原
cation methods of controller in practical projects.