Fires continue to occur in modern architecture, the people's lives and property has brought huge losses. In order to reduce the fire in the building automatic fire alarm equipment placed into a necessity. This paper discusses the automatic fire alarm system, the composition and working principle. The system will be collected through the fire alarm detector to the fire, fault and other signals sent to the sub-machine, Submachine re-transmission of such information will be sent to the fire alarm control, and then start from the controller, sound and light alarm display, alarm and other devices, and automatically print a fire information. This paper describes the overall structure of the fire alarm system, fire alarm control software in the design. Fire detectors using two-wire method to reduce the wall alignment, improve reliability, ease of construction and installation.