With　the　large-scale　uncertain　renewable　energy　connected　to　the　grid,　the　frequency　characteristics　of　the　power　grid　are　increasingly　complex.　Plagued　by　long　response　times　and　the　inability　to　accurately　track　frequency　regulation　commands,　traditional　thermal　power　units　call　for　urgent　improvement　in　the　performance　of　its　participation　in　frequency　regulation　of　automatic　generation　control　(AGC)　of　thermal　power　by　use　of　energy　storage.　Therefore,　firstly,　the　mathematical　model　of　frequency　regulation　performance　index　is　established　according　to　frequency　regulation　assessment　rules.　Besides,　considering　the　output　characteristics　of　the　energy　storage　system,　combined　with　the　improved　analytic　hierarchy　process　to　correct　the　weight　coefficient　of　the　frequency　regulation　sub　index,　the　first-stage　optimization　model　aiming　at　the　optimal　AGC　performance　is　constructed.　On　this　basis,　in　order　to　reduce　the　limit　crossing　and　storage　depth　charging　&　discharging　cases　at　the　state　of　charge　(SOC),　the　second-stage　optimization　model　is　constructed　in　order　to　minimize　the　SOC　deviation.　The　simulation　verification　shows　that　the　two-stage　frequency　regulation　method　proposed　in　this　paper　can　improve　the　frequency　regulation　performance　and　benefits　of　the　system　of　energy　storage　coordinated　with　thermal　power　unit,　while　reducing　the　energy　storage　in-depth　charging　&　discharging　cases　and　working　life　loss,　thus　improving　the　sustainability　of　frequency　regulation　auxiliary　service　of　energy　storage.　©　2024　Automation　of　Electric　Power　Systems　Press.　All　rights　reserved.