In this paper, to improve the adhesive strength of diamond films for the cemented substrates before depositing process, a new approach combined with heat-treatments and acid treatments was investigated. Relations between heat-treatments and surface morphologies, quality of diamond films and the adhesive strength were analyzed within the temperature range of 800~1 000℃. Heat treatment on the cemented substrate was an effective method to improve the adhesive strength for diamond films. With the heating process, large tungsten particles can be refined to small size which can enhance the “interlock functions” between diamond films and the substrate, and improve the density of secondary nucleation. The redundant metal cobalt was removed effectivelyto prevent the catalytic actions, which may cause the transformation from diamond to graphite. However, the adhesive strength was decreased with high temperature heating process subject to the holes left on the substrate surface. Results show that the samples heated at 900℃ owned the strongest adhesive strength and least compressive stress for diamond films.