The invention relates to a cluster electric water heater load aggregation method and device. The method comprises the steps that startup temperature and outage temperature of water heaters are adjusted according to a microgrid frequency fluctuation amount; based on the adjustment amount of the startup temperature and the adjustment amount of the outage temperature of the water heaters, a cluster water heater aggregation load power model is constructed; and the cluster water heater aggregation load power model is utilized to determine aggregation load power of the cluster water heaters. According to the technical scheme, energy conversion of a single water heater and the response law to microgrid frequency fluctuation are considered, load visual aggregation of the cluster electric water heaters is realized, and the aggregation load power model can be used for performing cluster control on regional water heaters to stabilize the microgrid frequency fluctuation.