With　the　further　open　of　the　electricity　market,　the　electricity　retailers　often　need　to　configure　appropriate　amount　of　energy　storage　to　reduce　the　operation　cost.　In　order　to　solve　this　problem,　an　energy　storage　capacity　optimization　model　is　proposed　to　minimize　the　operation　cost　of　the　electricity　retailers　under　the　participation　of　multiple　flexible　resources.　The　adjustable　resources　and　operation　cost　of　the　electricity　retailer　is　analyzed.　And　the　economic　model　of　energy　storage　allocation　for　the　electricity　retailer　is　built　based　on　the　life　cycle　cost.　In　order　to　solve　the　sequential　decision-making　model,　the　Soft　Actor　Critic　algorithm　(SAC)　is　used　to　find　the　optimal　storage　capacity　allocation　for　electricity　retailer　based　on　grid　search.　Finally,　the　proposed　model　is　verified　by　various　simulations.　©　2021　IEEE