The invention discloses a method and system for configuring the energy storage capacity of a power grid under the constraint of frequency safety, which comprises the steps of constructing typical operation modes applicable to time domain simulation of static load fluctuation and a first-level standard fault and a second-level standard fault of the power grid; carrying out time domain simulation inallusion to the three typical modes; analyzing whether the problem of frequency out-of-limit exists or not under the current energy storage configuration capacity of the power grid in allusion to thesimulation result; respectively carrying out iterative simulation to obtain the minimum energy storage capacity under the primary frequency modulation and emergency control requirements of the powergrid; and determining the minimum configuration capacity of energy storage under the constraint of frequency safety of the power grid. The minimum energy storage capacity configuration requirement forensuring the frequency safety of the power grid is provided according to different positions of energy storage in a frequency defense system of the power grid, thereby providing technical support forthe energy storage capacity planning of the power grid.