Abstract: Because the micro structures and mechanical properties were nonuniform in the aluminium alloy welded joint, it was necessary that the local mechanical properties was measured accurately for the assessment of the mechanical properties of whole welded joint and the improvement of the welded technique.In this paper, the micro structures and hardness of the automobile 5052 aluminium alloy were analyzed, at the same time, the small ball punch test was put forward to investigate the local mechanical properties of material, which combined with a revised FEM algorithm with ABAQUS computer code.The constitutive properties of the local material was indirectly obtained by the numerical model which was a special revised iterative process and worked out the true strain-stress curves for an unknown material.The process accuracy was validated by the uniaxial tension test.The results show that the distribution character of its curve was similar with that of the welded joint hardness distribution, and the worst local mechanical properties of aluminium alloy welded joint was located around the fusion line.