Aiming at the current disadvantages of fire alarm in middle and high-rise buildings, such as unstable wireless system signal, and difficult maintenance of complex wired wiring in the later stage, this paper uses LoRa long-distance transmission technology to design the Internet of Things cloud building alarm system. The system uses the data cloud platform to monitor the sensing information of each node. Experiments show that the system can run stably for a long time and can quickly and accurately perceive the flame data of each node.