Although　welding　structures　with　Ni/Al　dissimilar　metals　have　great　application　potential,　the　interfacial　metallurgy　is　not　fully　understood.　The　interfacial　microstructures　and　its　formation　mechanisms　of　the　Ni/Al　joint　were　investigated　by　controlling　the　laser　beam　offset　toward　to　Al　side.　Two　modes　of　Ni　dissolution　and　melting　were　discovered　during　the　laser　welding.　When　the　offset　was　relatively　big,　the　Ni　dissolved　to　the　weld　first　and　then　the　intermetallic　compounds　(IMCs)　formed　during　the　welding.　The　IMCs　consisted　of　Al3Ni2　in　the　precipitation　and　Al3Ni　in　the　peritectic　reaction　and　precipitation.　The　weld　was　divided　into　hypereutectic　reaction　zone　(Hyper-ERZ)　near　to　the　interface　and　hypoeutectic　reaction　zone　(Hypo-ERZ)　far　from　the　interface.　When　the　offset　was　relatively　small,　the　Ni　surface　layer　adjacent　to　the　weld　melted　first　and　then　complex　interfacial　reaction　occurred.　The　IMCs　were　composed　of　AlNi　in　the　precipitation,　Al3Ni2　and　Al3Ni　in　peritectic　reactions　and　precipitations.　The　melted　layer　transformed　to　double　peritectic　reaction　zone(DPRZ).　The　weld　consisted　of　Hyper-ERZ.　With　increasing　the　offset,　the　tensile　strength　of　the　joints　increased　first　and　then　decreased.　The　highest　value　was　up　to　136.2　MPa,　which　is　80　%　of　5052　Al　tensile　strength.