Seeding substrates with diamond nanocrystals has been considered to be a promising nondestructive pretreatment method for growth of diamond films. However, its application is strongly impeded by the segregation of diamond nanocrystals on substrates. In the present study, we suggest a very simple but effective seeding way ("sandwich" (SW) seeding way) to prevent nanocrystals from segregation. By the SW seeding way, the diamond nanocrystals can be nearly uniformly dispersed on Si substrates with the areal density of the order of 108cm-2. On the nano-seeded Si substrates the continuous and homogeneous diamond films can be successfully fabricated using a microwave plasma enhanced chemical-vapor-deposition (MPECVD) equipment. The cross-sectional transmission electron microscopy (TEM) images reveal that compare with the diamond films grown on the Si substrates pretreated by the conventional scratching method, the films deposited on the nano-seeded Si substrates present a much flatter interfacial structure, suggesting that the SW seeding way can effectively reduce the interface coarseness.