The WC-6%Co(mass fraction) substrate surfaces were chemically pretreated with the two-step etching method, using Murakami reagent for 3～7min, and then an φ(HNO3)∶φ(HCl)=4∶1 solution for 1～15min. Diamond films were deposited on the substrates by a hot-filament chemical vapor deposition reactor. The results show that the Co content of the substrate surfaces can be reduced from 6% to 0.12% within the etching depth of 5～10μm, the surface roughness of the substrates is increased up to Ra=1.0μm, as well as the substrates hardness is decreased from HRA 89.5 to HRA 84.2 after the two-step etching. A slight preference towards {111} orientation can be observed from the XRD patterns and SEM micrograph of diamond film on WC-6%Co sample. The morphology of small rice-like ballas diamond was observed on the WC-6%Co substrates. A typical Raman spectrum with a sharp peak at 1332cm-1 for the diamond film indicates that the deposited films are good-quality polycrystalline diamond. The indentation testing shows that the adhesion between diamond film and the substrate after HF CVD deposition is good.