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.