Diffracted wavefront aberration and distribution of far-field diffraction light are important manifestation for the quality of pulse compression gratings with a large aperture. In order to optimize the energy distribution of far-field light spots of splicing gratings, this paper proposes a parallel splicing method for gratings. Grating parallel splicing and grating aligned splicing are simulated under different aberrations, and the energy distribution of far-field diffraction light spots of the corresponding wavefront is calculated. The statistical results show that the peak valley (PV) value of the wavefront of gratings with parallel splicing is smaller than the that of gratings with aligned splicing. However, the energy distribution of the far-field scattering light spots of gratings is related to the type of aberrations and the modes of splicing. Experiments are carried out on gratings with holographic exposure splicing, and the results show that grating parallel splicing method can not only reduce the PV value of the -1st order diffracted wavefront aberration, but also improve the energy concentration of far-field diffraction light spots. Therefore, it provides a new method for holographic splicing gratings.