Comparing with ordinary ploycrystalline materials sized to μm grade, the slip morphology of the coarse grained polycrystalline pure Al is characterized by: (1) several slip domains occur in a grain, and in same domain, several slip systems operate at same time or one after another intensely, a beautiful and neat slip pattern is forming on the specimen surface; (2)for high-∑value coincident and random grain boundaries , the grain boundary affecting zone (GBAZ), about 50--120 μm wide, is favourable site to form intergranular crack at early fatigue life easily, and migration or slide of the boundaries were often observed. While low ∑--value near-coincident grain boundaries show a higher degree of slip continuity and strain compatibili-ty than high ∑--value ones. Intergranular crack is not easily nucleated at low ∑--value near--coincident boundaries; and (3) due to suppression of grain boundary slip at triple grain boundary node, the high ∑--value and random grain boundary among the three boundaries of tricrystal crack easily during cyclic deformation.