Diamond film has been deposited on stainless steels using hot filament chemical vapor deposition by applying Al/AlSiN as interlayer to improve the adhesion strength. The results show that diamond film exhibits good adhesion performance in the case of 3.4 at.% of Si contained in the AlSiN interlayer. Moreover, the film is smooth with small roughness of Ra 58.3699 nm. Grazing incidence X-ray diffraction pattern indicates that AlSiN solid solution has been formed, which prefers more carbon atoms to diffuse into the AlSiN layer. Accompanying by the diffusion of chromium atoms from the steel substrate into the interlayer, more chromium carbide formed at Al/AlSiN interface, which strengthens the weakest point of the film by decreasing stress concentration and providing mechanical interlocking, improving the adhesion of diamond film. At Si content equal to or higher than 5.4 at.% in the interlayer, amorphous Si3N4 precipitates at the grain boundaries, which decreases the volume of grain boundaries, resulting in the decrease of carbon diffusion rate. Consequently, a small number of carbides form at Al/AlSiN interface, weakening the adhesion of the film.