Nowadays, there are some problems exist in remote monitoring of IoT fire control system, such as bad real-time performance, difficulty access of massive nodes, the security problems arisen due to the lack of standardized authentication and registration mechanism. In view of the problems above, this paper proposes a networking mechanism of fire monitoring system based on IoT. This mechanism uses public IoT cloud hosting service to meet the needs of mass nodes access. System architecture is Publish/subscribe mode based on lightweight MQTT protocol, so it can meet the real-time data transmission. We add the node certification mechanisms in the process of node registration and encrypt the message in the process of transmission. This standardized network-access mechanism improves the security of the whole system. Through short-term testing, this network mechanism can well solve the above problems in the current fire monitoring system. Due to its scalability and high stability, this network mechanism can be widely used in online monitoring of large-scale public places and buildings.