Embodiments of the present disclosure provide a method and an Internet of Things (IoT) system for diagnosing accuracy of a smart gas ultrasonic meter. The method is implemented by a smart gas device management platform of the IoT system for diagnosing accuracy of the smart gas ultrasonic meter. The method includes: acquiring gas attribute data of gas passing through a metering device based on a distributed sensor deployed in a gas pipeline network; determining a first accuracy risk of the metering device through performing pre-diagnosis on the metering device based on the gas attribute data and metering device information; determining a second accuracy risk of the metering device through performing precision diagnosis on the metering device based on a pre-diagnosis result; and displaying detection indication information to the smart gas device management platform based on a precision diagnosis result.