Despite the fact that fracture behaviors of pre-cracked metal plates were investigated by the crystal plasticity finite element method (CPFEM), the thickness effect on their micro-fracture behaviors is still not clear because of the different out-of-plane constraints. Here, mechanical properties and micro-fracture patterns of pre-cracked aluminum plates with different thicknesses are obtained by experiments, as well as by CPFEM combining with two damage criteria. First, finite element models are constructed based on grain morphologies of specimens achieved by electron back scattered diffraction experiments. Next, some key parameters required in CPFEM and two damage criteria are determined by fitting experimental stress–strain relationships. In particular, the factors affecting accuracy of FE predictions are clarified by CPFEM. Finally, thickness-dependent micro-fracture mechanisms of two different damage criteria in pre-cracked aluminum plates with various thicknesses and crack lengths are revealed by comparison with the experimental results and CPFEM. This investigation should be of great help for understanding thickness-dependent micro-fracture mechanisms of metal and other material plates.