With　the　large-scale　uncertain　renewable　energy　connected　to　the　grid,　the　frequency　regulation　demand　is　growing　day　by　day,　and　there　is　a　great　need　to　use　energy　storage　to　improve　the　automatic　generation　control　(AGC)　performance　of　the　thermal　power　to　meet　the　grid　frequency　regulation　requirements.　Therefore,　a　two-stage　optimization　method　considering　AGC　performance　and　state　of　charge　(SoC)　control　for　energy　storage　coordinated　with　thermal　power　unit　in　AGC　is　proposed　in　this　paper.　Firstly,　the　AGC　performance　assessment　index　constraints　are　linearized,　which　is　used　to　establish　the　first　stage　optimization　model　of　the　joint　system　participation　in　frequency　regulation.　Further,　to　reduce　the　depth　charging/discharging　situation　of　energy　storage,　the　second　stage　optimization　model　is　constructed　with　the　objective　of　minimizing　the　SoC　deviation.　Finally,　the　simulation　result　shows　that　the　proposed　two-stage　optimization　method　can　improve　both　AGC　performance　and　sustainability　of　energy　storage,　and　effectively　reduce　the　loss　of　energy　storage　working　life.　©　2023　IEEE.