A model is proposed for the analysis of possible errors in a tiled-grating pair compressor. By using the method of Fourier optics, the process of a chirped pulse's passing through a misalignment tiled-grating pair compressor and an ideal lens is studied and the integral expression of light field on focal plane is obtained. The effects of possible errors on focal spot intensity distribution are analyzed in detail by the numerical simulation. The results indicate that possible errors must satisfy Δx-nd