In the application of nanometer lithography, two gratings with similar periods were chosen for alignment marks on the wafer and mask respectively. Then light was modulated by these two gratings when they traveled through two alignment marks, and some phenomenon such as diffraction and interference occurred so that regular and periodic-distributed moiré patterns were formed in the process of alignment. Because the fringe with magnified period versus periods of two gratings has high sensitivity to represent relative movement of two gratings on wafer and mask, it has a good prospect in the application of alignment of lithography. Theoretical analysis and deduction of the regularity of approximate spatial distribution of moiré patterns resulting from superposition of two proximity gratings with close frequencies were performed in the viewpoint of Fourier Optics. Furthermore, a set of alignment marks which could double the sensitivity were designed. Approximate mathematical model of complex amplitude of interferometric fringes and the process of alignment of lithography were verified through simulation.