The present invention provides a gas data transmission method based on a compound Internet of Things (IoT) and an IoT system. The method includes: sending, by a main sensor network sub-platform in a plurality of sensor network sub-platforms, gas data to a management platform; storing, by auxiliary sensor network sub-platforms, the gas data; when the management platform cannot receive the gas data sent by the main sensor network sub-platform, sending, by the management platform, interactive data to the main sensor network sub-platform; and when the main sensor network sub-platform does not respond to the interactive data, disconnecting, by the management platform, from the main sensor network sub-platform and establishing a connection with one auxiliary sensor network sub-platform to receive the gas data stored by the auxiliary sensor network sub-platform.