Abstract: The“saddle effect”of crack growth caused by the increase of specimen thickness is a representation of the connection between thickness and the stress-strain field at the three-dimensional crack end. Without this internal connection mechanism and rule, the damage tolerance assessment of large thickness and variable thickness plates in large mechanical equipment based on traditional models must have great risks. With large thickness aluminum alloy plate as the research object, the current research status of crack propagation related issues is summarized and analyzed from three aspects, including the relationship between three-dimensional stress-strain field at crack end and crack propagation morphology, thickness effect of fatigue crack propagation, crack propagation mechanism and model under the joint of corrosion and fatigue. The key problems in studying the fatigue crack propagation characteristics of aluminum alloy plate with high thickness are discussed.