ZnO/GaN　in-plane　heterojunction　with　three　contacted　modes　(Zn-N,　Ga-O　and　both　Zn-N　and　Ga-O,　named　He1,　He2　and　He3,　respectively)　is　constructed.　At　the　same　time,　the　vacancy　defects　(VZn,　VN,　VGa　and　VO)　are　introduced　at　the　interface　of　the　in-plane　heterojunction.　Their　electric,　magnetic　and　adsorption　properties　with　vacancy　defects　are　analyzed　based　on　density　function　theory　(DFT).　After　constructing　the　heterojunction,　the　effective　mass　of　holes　obviously　increases　and　leads　to　higher　separation　efficiency　between　electrons　and　holes.　Band　structures　show　that　VZn　and　VGa　change　the　magnetism　of　He3　and　total　magnetic　moment　(M)　are　1.69　μB　and　2.73　μB,　respectively.　He3　exhibits　semiconducting　conductivity　with　VZn　and　semi-metallic　conductivity　with　VGa.　In　order　to　explore　the　application　in　gas　sensing　field,　the　electric　and　adsorption　characteristics　of　He3　(with　VZn　and　VGa)　for　CO2,　SO2　and　NO2　gas　molecules　are　combined　to　analysis.　Ead　of　the　He3　for　SO2　and　NO2　is　higher　than　CO2　adsorption.　In　addition,　the　magnetic　properties　of　He3　(with　VZn　and　VGa)　change　drastically　after　adsorbing　SO2　and　NO2,　which　proves　that　He3　is　more　sensitive　to　SO2　and　NO2　than　CO2.　These　results　demonstrate　that　He3　not　only　exhibits　unique　electrical　and　magnetic　properties,　but　also　has　potential　applications　in　SO2　and　NO2　gas　sensors.　©　2022　Elsevier　B.V.