Grating tiling technology using small aperture multilayer dielectric coating diffraction gratings to form large-aperture high-damage threshold gratings is the key technology to solve the output energy of the PW laser system. There are errors of five degrees of freedom between each adjacent pair of gratings within a tiled-grating system, affecting the spatial and temporal property of the laser beam. The authors express the relationship of far-field intensity distribution as the function of individual error by analyzing the effect of tiling gratings errors on the laser beam spatial distribution with Fraunhofer diffraction method and simulate it with numerical method. The results indicate the distortion in the pulse shape caused by angle error is negligible, the piston errors including in-plane shift and out-of-plane shift errors are the critical effects on the far-field intensity distribution.