As　the　most　serious　and　frequent　power　quality　problem,　voltage　sag　significantly　impacts　the　electricity-gas　integrated　energy　system　(EG-IES)　through　sensitive　coupling　equipment.　In　order　to　reduce　the　economic　loss　of　the　EG-IES　system　caused　by　voltage　sags,　this　paper　proposes　an　optimal　configuration　method　for　the　EG-IES　coupling　equipment.　The　paper　first　analyzes　voltage　sag　impacts　in　the　normal　operation　of　EG-IES　through　coupling　equipment.　Then,　tolerance　characteristic　curves　of　the　compressor　and　gas　turbine　are　presented,　and　an　economic　loss　model　caused　by　voltage　sag　is　established.　Finally,　an　optimal　configuration　model　is　established　considering　the　cost　of　coupled　equipment　and　voltage　sag　loss.　The　method　is　applied　to　the　EG-IES　composed　of　IEEE14　nodes　and　gas　network　11　nodes,　proving　that　the　method　can　effectively　reduce　the　loss　of　EG-IES　caused　by　voltage　sags　while　considering　the　equipment　installation　cost.　©　2023　IEEE.