Based on the Shannon sampling theory and Fourier transform analysis, analysis on the effects of non-synchronous sampling on the reconstructed image of digital hologram is given by the simulation experiment of digital holographic grating. The results indicate that the phenomena of low frequency modulation of the transmission function will be more obvious with the increase of grating′s spatial frequency; the extent of spectral leakage is determined by the deviation of non-synchronous sampling, but has nothing to do with the spatial frequency of the holographic grating itself. Finally, the experiment of digital hologram apodization using the Tukey window function shows that the apodization method can suppress the fluctuation of reconstructed wave front caused by the spectral leakage.