Introducing the tip-tilt and piston error as the parameter and defining the aperture function of the tiled-grating, far-field property was analyzed with Gaussian beam incidence using the theory of Fourier angular spectrum. The results showed that the output beam was Gaussian while the center of the envelope shifted, the shift magnitude was determined by angle errors and beam size. The phase difference caused by piston error translated with the tiled-grating compressor, the focal spot was affected by both non-integral number of grating space and out-of-plane piston error. Numerical simulation showed the effect on the spatial characteristic of the tiled-grating compressor due to alignment errors.