The object of this research is building automation control system and to design the system by means of the computer application. First, I analyze the operating principle of the automatic monitored control system based on the computer technology, and I find that with the help of Ethernet switching engineering we can solve the problem about high network load and transmission delay of traditional building automation control system. At the same time, I design the overall structure of the automatic monitored control system. Then I learn the hardware control system and the implementation of the software, and the mainly representative object is the central air-conditioning control system. As the core component of the control system, PLC’s hardware and transducer are chosen. And I design the process of software control, data acquisition, communication device and other modules. Meanwhile, I finish the design of the procedure of PLC master control module and realize the software monitoring and control with the host computer software. Finally, I explore the remote monitoring software based on internet, and improve some problem like the spread of information during the monitoring in the past and develop the auxiliary function of short message reminder with the end of the integrated structure, idea and the structure based on the computer application and the design of the key part.