The tensile strength and impact properties at low temperature were investigated on Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er alloy for cold rolled, warm rolled and fully annealed samples. The original microstructures, tensile fracture and impact fracture were observed using electron back-scattered diffraction(EBSD), transmission electron microscope(TEM) and scanning electron microscope(SEM) in order to analyze the effects of microstructure on tensile property and impact properties. The results showed that, with the decreasing of testing temperature, the stresses are drastically increased as well as the impact properties. The tensile strength and impact property of warm rolled alloy with more sub-boundaries has a higher strength and impact property which realized the matching of high strength and toughness.