Grid　has　been　mainly　used　in　the　high　performance　computing　area.　The　properties　of　geographic　information　and　its　related　computing　properties　determine　that　the　grid　technology　has　great　potential　in　the　construction　of　geographic　information　service　system.　In　this　paper,　based　on　the　analysis　on　the　character　of　grid　technology　and　geographic　information　service　system,　the　concept　of　the　＂geographic　information　service　grid＂　(GISG)　is　put　forward.　And　the　four　layer　model　to　construction　of　GISG　is　also　put　forward,　which　includes　4　layers,　i.e.　the　computing　service　grid　layer,　the　geographical　data　service　grid　layer,　the　geographical　information　service　grid　layer　and　the　geographical　knowledge　service　grid　layer.　In　the　next　part,　the　key　technologies　to　construct　GISG　are　discussed.　In　the　construction　of　GISG,　the　communication　protocol　and　language　are　the　key　parts　of　the　whole　system.　The　application　of　GridFTP　protocol　and　GML-based　geographic　information　service　grid　architecture　are　studied　in　this　paper.