Seawater　hydraulic　system　which　are　environmentally　compatible　with　automatic　pressure　compensation　are　suitable　for　working　in　deapsea　water　and　maintaining　the　marine　environment.　In　this　paper,　Seawater　hydraulic　system　structure　will　be　converted　into　complex　network　model.　According　to　basic　parameters　in　complex　network　theory,　complex　network　model　of　seawater　hydraulic　systems　are　constructed.　Based　on　these　models,　characters　of　Seawater　hydraulic　system　are　analyzed.　Based　on　complex　networks　theory,　definition　of　vulnerability　of　Seawater　hydraulic　system　is　proposed.　Moreover,　structural　vulnerability　of　train　Seawater　hydraulic　system　is　studied.　This　work　could　give　support　for　safety　of　Seawater　hydraulic　system.　©　2015　IEEE.