The invention provides a fire storage system and an energy storage system AGC frequency modulation method and device. The method comprises steps that when the fire storage system is in an automatic power generation control AGC frequency modulation mode, firstly, a frequency modulation power command and a state of charge SOC of an energy storage system in the fire storage system are obtained; secondly, according to the FM power command and the SOC, the state relationship between the FM power command and the SOC is determined; thirdly, according to the state relationship, the corresponding frequency modulation strategy is formulated; the frequency modulation strategy includes repair strategy, the repair strategy is as follows, when the state relationship is out of the intervention control scope and the FM power command is within the positive dead scope, the energy storage system is controlled for performing forward operation till the SOC transforms to a corresponding near limit value ofthe ideal scope; the SOC of the energy storage system is made to tend to an ideal scope, SOC deviation of the energy storage system is avoided, moreover, the frequency modulation algorithm of the energy storage system is guaranteed to be effective, that is, the energy storage system effectively assists a thermal power unit to complete an AGC frequency modulation task, and AGC FM performance is improved.