We　propose　a　method　to　construct　Hopf　insulators　based　on　the　study　of　topological　defects　from　the　geometric　perspective　of　Hopf　invariant　I.　Firstly,　we　prove　two　types　of　topological　defects　naturally　inhering　in　the　inner　differential　structure　of　the　Hopf　mapping.　One　type　is　the　four-dimensional　point　defects,　which　lead　to　a　topological　phase　transition　occurring　at　the　Dirac　points.　The　other　type　is　the　three-dimensional　merons,　whose　topological　charges　give　the　evaluations　of　I.　Then,　we　show　two　ways　to　establish　the　Hopf　insulator　models.　One　approach　is　to　modify　the　locations　of　merons,　thereby　the　contributions　of　charges　to　I　will　change.　The　other　is　related　to　the　number　of　defects.　It　is　found　that　I　will　decrease　if　the　number　reduces,　while　increase　if　additional　defects　are　added.　The　method　developed　in　this　study　is　expected　to　provide　a　new　perspective　for　understanding　the　topological　invariants,　which　opens　a　new　door　in　exploring　and　designing　novel　topological　materials　in　three　dimensions.