There are two key problems that hamper the batch production and widespread applications of the diamond coated WC-Co carbide products. One is low adhesion between the substrates and diamond film, the other is difficult to control the quality of diamond film. Both are closely related with the element Cobalt. To solve the problems, it is necessary to find out and master the correlativity and change regularity of the influence factors on diamond nucleation, growth and properties on WC-Co carbide, which are correlative with not only the diamond deposition process but also pretreatment process. The research contents and methods of the paper are as folio wings:(1)For one-step chemical pretreatment, aqua regia was employed as corrosive solution for the erosion of cobalt, the variation of cobalt concentration in aqua regia with etching time was determined by AAS (atomic absorption spectroscopy). Diamond films were deposited on the WC-Co substrates by a direct current arc discharge plasma chemical deposition reactor. And carbide from various producers were investigated to testify the result of one-step study.(2)For two-step pretreatment, the correlations between the etching extent of WC and the adhesion between diamond film and substrate, were studied in this paper.(3)The substrate surface properties and properties of diamond coatings were characterized by means of EDX (Energy dispersive X-ray spectroscopy), SEM (scanning electron microscope) and so on.The conclusion of the study were drawn as folio wings:(1)The amount of cobalt eroded from WC-Co carbide were closely related with the quality of diamond film, and the adhesion between diamond film and carbide substrate. The result shows that 90 seconds is testified to be an optimum point for acid etching. Shorter time may result in poor nucleation of diamond, sometimes even no diamond can form. Longer time may result in poor adhesion between diamond film and substrates.(2)The conclusion drawn above was testified employing carbide of the same type from different producer. And result matches the conclusion.(3)The result of two-step pretreatment showed that adhesion between diamond film and carbide was highly improved.