The nucleation and growth process of diamond film on porous silicon in a hot-filament chemical vapor deposition system were investigated. The nucleation density of 3.6 x 10(7) cm(-2) was obtained. We find that almost all of the nuclei occur at the edge of the etched pores, and the continuous diamond films are successfully deposited without seeding diamond particles. The characters of diamond films were determined by scanning electronic microscopy, Raman spectra and X-ray photoelectron spectroscopy. No strains are found in diamond films, and no intermediates are found between the films and porous silicon substrates.