Abstract: Isothermal hot compression test of 2E12 aluminum alloy was operated on Gleeble-1500 thermal simulation test machine. Microstructure after hot deformation of the alloy was observed by TEM and FE-SEM. Dynamic softening mechanism and microstructure evolution regular of the alloy during hot deformation under different conditions were studied. The results show that when deformation temperature was below 400 ℃, the main softening mechanism of the alloy was the dynamic recovery. When deformation temperature was above 450 ℃, the major softening mechanism was continuous dynamic recrystallization(CDRX). The major nucleation mechanism of the alloy dynamic recrystallization was subgrain turning merging and alloy nucleated preferentially along original grain boundary.