Abstract: In order to analyze the effects of fixed and random wave aberration on the large-aperture mosaic compression gratings, by numerical simulation, the far-field characteristics for referenced gratings were studied. On the basis of the precise evaluation criterion, the tiling accuracy of the mosaic gratings was obtained. The results showed that the maximum piston error of the tiling precision was about 0.26 grating period when the wave aberration of sub-gratings was 1.0λ. After manual intervention, the maximum piston error was about 0.42 grating period and the maximum tip-tilt error was 0.71μrad approximately, which were both lower than before. The research is benefit for the improvement of high energy picosecond laser device.