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The Al2O3 reinforced 7055 aluminum matrix composite was subjected to pulsed magnetic field treatment with different induced intensity (B). The dislocation density in composites increases when the B rises from 0,1T, 3T to 5T. It is attributed to the enhancement of strain energy of dislocation and the transition from S to T for the radicals between the dislocation and pinning center. Meanwhile, the orientation tendency of intragranular precipitates is lowered, together with the increase of amount and size. For the precipitates at grain boundary, the morphology has transformed from continuous to disconnected states. The precipitation amount has been decreased while the size increased. It is highlighted that the precipitation free zone can be found. It is analyzed that the magnetic field accelerate the diffusion of solute atoms and vacancies. The increased distortion energy and internal stress facilitate the precipitating and growing process. As for the mechanical properties, the trend displays as the first rise followed by falling. When B equals to 3T, the tensile strength, elongation and micro hardness arrived at 548.04MPa, 17.235% and 122.4HV, which are increased by 10.3%, 16.2% and 20.7% separately compared to the initial sample without any magnetic field treatment. The strengthening mechanisms are attributed to the dislocation strengthening and second phase strengthening.