In　recent　years,　the　application　of　Electric-Gas　Integrated　Energy　System(EG-IES)　has　continued　to　develop,　the　coupling　and　connection　between　energy　sources　have　become　more　and　more　close,　and　the　interaction　between　power　system　and　natural　gas　system　has　become　complex.　The　change　of　power　system　network　state　will　not　only　affect　its　own　system,　but　also　affect　the　natural　gas　system　through　coupling　devices,　which　will　cause　huge　economic　loss　when　it　is　serious.　This　paper　first　analyzes　the　impact　of　voltage　sag　events　in　the　power　system　on　the　electricity-gas　integrated　energy　system,　and　then　considers　the　natural　gas　system　user　economic　loss　assessment　based　on　the　process　parameter　immune　time　curve　to　provide　a　basis　for　subsequent　voltage　sag　control　methods.　Finally,　an　electric-gas　integrated　energy　system　composed　of　IEEE14-node　and　10-node　natural　gas　systems　is　selected　as　an　example　to　verify　the　correctness　and　effectiveness　of　the　evaluation　method.　©　2021　IEEE.