The compression of amplified chirped pulse by parallel grating pair is an important step in generating ultrashort ultrahigh intensity pulse. In this paper, for single pulse compression (30 min/shot), two methods are proposed in detail for the alignment of dual grating with large caliber (350 mm×185 mm×60 mm) and dense grooves (1760 lp/mm). The shortcoming and advantage of two methods are compared with each other. In addiation, the related problems of the alignment are discussed.