Based on the spectrum analysis of digital hologram illuminated with spherical wave in the course of object wavefront reconstruction with selectable magnification, the method of eliminating the influence of zero-order diffraction is proposed, which uses highpass filter before illuminating hologram with reconstruction wave. The theoretical simulation and experimental result of wavefront reconstruction are given from two aspects: scattering and undiffused light from object surface. The result shows that the interference of the reconstructed image can be eliminated effectively when scattering occurs on the surface. However, when the surface is a smooth plane, much stricter condition should be needed in order to get a completely reconstructed image.