The perpendicular magnetic anisotropy (PMA) of the CoFeB/AlOx/Ta structure and the AlOx/CoFeB/Ta structure with different thicknesses of both CoFeB and AlOx is studied. Magnetization curves show that the CoFeB/AlOx/Ta structure has a clear perpendicular magnetic easy axis while the AlOx/CoFeB/Ta structure does not. The cause of the asymmetrical phenomenon in the symmetric structures is analyzed. Dependence of the perpendicular coercivities on the thicknesses of CoFeB and AlOx shows that both of them can affect the strength of the PMA originating from the interfacial interaction. This work will be meaningful for the fabrication of the AlOx-based perpendicular magnetic tunnel junctions.