The embodiment of the present disclosure provides a method and an Internet of Things system for monitoring a smart gas pipeline network based on an ultrasonic flowmeter. The method is implemented by a smart gas management platform of the Internet of Things system, including: acquiring distributed ultrasonic data for least at one moment, the distributed ultrasonic data including ultrasonic data acquired by the ultrasonic flowmeter and the ultrasonic flowmeter being deployed at at least one detection position of the gas pipeline network; determining a leakage risk of at least one preset point of the gas pipeline network based on the distributed ultrasonic data; and generating and sending warning information to a user based on the leakage risk.