In order to meet the demands of high-accuracy alignment with large measurement range in proximity lithography, a method based on composite gratings is introduced. The composite gratings consist of small-period gratings with slightly different periods and large-period gratings with small range which are orthogonal to the smallperiod ones. Fine alignment is realized by high-precision phase analysis on moiré fringes while coarse alignment is achieved by obtaining the position of large-period gratings directly. Since the different-direction gratings are orthogonal to each other, there will be no influence on extracting frequency spectrum by applying Fourier transform. By analyzing the phase variations of small gratings’moiré fringes and the intensity of large-period gratings, substrate and mask can be aligned with high accuracy and large measurement range. Furthermore, the relation between the offsets of substrate and mask and the position changes of the two composite gratings are derived. An analysis of the built model is performed via simulation to show that the accuracy can reach 16.5nm while considering the noises; and an experiment is also conducted to verify the effectiveness of the proposed method and the accuracy can reach 30.19 nm.