The present disclosure provides a method and system for flood early warning in a smart city based on Internet of Things (IoT). The method includes: obtaining precipitation information of a target area within a target time period through a meteorological management platform, obtaining drainage capacity information of the target area through a water affairs platform, determining regional ponding information of the target area in the target time period based on the precipitation information and the drainage capacity information, and generating a first flood early warning information of the target area based on the regional ponding information.