The embodiments of the present disclosure provide an alarm-based prevention and control method and an Internet of Things (IoT) system for a safety risk of smart gas, including: obtaining gas monitoring data based on a data acquisition instruction, and determining whether a gas leakage occurs; in response to a determination that the gas leakage occurs, generating a control instruction based on a fan operation strategy to control operation of a fan, and obtaining the gas monitoring data under the fan operation strategy, the fan being configured to remove leaking gas and assist in determining a type of the gas leakage; and generating a notification instruction based on the gas monitoring data in conjunction with an operating strategy of an indicator light, and controlling the indicator light to issue an alarm notification based on the notification instruction.