By　the　first-principles　calculations　based　on　the　density　functional　theory,　the　tensile　strength　of　Al　metal　with　dislocations　of　twist　grain　boundaries　(GBs)　is　predicted　from　its　electronic　structure　to　its　essential　mechanical　properties.　The　results　show　that　the　theoretical　tensile　strength　for　Al　twist　GB　is　about　8.73GPa　and　it　is　less　than　that　for　Al　glide　GB(9.5GPa)　(Phys.　Rev.　B　75,　174101　(2007)).　However,　its　fracture　strain　for　Al　twist　GB　is　24%　and　16%　more　than　that　for　Al　glide　GB.　It　suggests　that　the　mechanical　properties　of　the　metal　can　be　greatly　improved　by　experimentally　modulating　its　defect　or　dislocation.　Furthermore,　the　physics　of　the　fracture　of　Al　twist　GB　is　analyzed　by　the　distributions　of　charge　density　and　the　changes　of　bond　length,　and　it　is　found　that　the　facture　appears　in　the　GB.　Our　theoretical　predictions　can　play　an　important　role　in　guiding　the　improvement　of　mechanical　properties　and　structural　designs　for　Al　metal.