Contemporary chirped-pulse-amplified high-power laser systems rely on meter-sized diffraction gratings for pulse compression. Fabricating large gratings is a bottle-neck problem. We developed a multiple-holographic-exposure method to fabricate large monolithic gratings. In consecutive exposures, the attitude of the photoresist-coated substrate is monitored and adjusted by using two interferometers with a He-Ne laser, and the relative position between the substrate and the exposure interference fringes is adjusted by using the interference fringes between the diffraction orders of the latent grating with the exposure beams as the incident beams. A mosaic grating with a size of 80×50 mm2 was fabricated, and the wavefront aberration of the 1st-order diffraction wavefront in the mosaic area is better than /10 PV @633 nm.