Microstructural evolution of the semisolid Al-4Cu-Mg alloy fabricated by strain induced melting activation (SIMA) at different deformation temperatures and strain rates during semisolid deforming were investigated. The experimental results show that the grain size increases with the increase of deformation temperature and decreases with the increase of height reduction. Fractal dimension decreases with the increase of deformation temperature and increases with the increase of height reduction after an early drop. Grain size decreases with the increase from 0.001 s-1 to 0.1 s-1 of strain rate, but increases slightly with the increase from 0.1 s-1 to 1 s-1 of strain rate. The lower the strain rate, the greater effect of strain rate on grain size. Fractal dimension increases with the increase of strain rate.