Compression tests were performed at temperatures from 350 to 450 °C with different strain rates of 1.0×10−2 and 1.0×10−1 s−1. The microstructures of deformed samples were investigated by electron backscatter diffraction (EBSD). Microstructure observations indicated that under present deformation conditions, fraction of new grains increases with the Z value. It was found that different nucleation mechanisms for DRX were operated in hot deformed 7055 alloy, which was closely related to deformation condition. DRX nucleation and development were discussed in consideration of bulging of original grain boundaries and occasional subgrain rotation near the grain boundaries. Discontinuous dynamic recrystallization (DDRX) which occurred in a local area was also proved to be a nucleation mechanism at higher Z value for 7055 alloy.