The surface and backside morpologies of diamond thin film as well as the surface morphologyof the cobalt cemented tungsten carbide (YG8) insert after deposited using D. C. plasma jetCVD method were observed by SEM. The cross- sectional morphology and microstructure ofa CVD diamond thin film grown onto the cemented carbide insert were studied by means ofTEM. Fourier transformated laser Raman spectrometry was also used to characterize the structurecompositions of the diamond thin film deposited and the cemented carbide insert surface afterdiamond thin film delaminated. The results show that there exists a thin layer of graphite carbon(tens of nanometers) at the interface of a diamond thin film coated cemented carbide insert. Ithas been seen, However, that diamond particles can be grown directly onto WC crystals at partialzones. Typical cross-sectional morphology of a diamond thin film coated cemented carbide insertformed on the basis of pertreatment processes such as chemically cobalt-removed and plasmaetchingdecarbonized treatments is as follows: diamond thin film, graphite carbon thin layer, small WCgrains layer, retained decarbonized layer (W and n phases), YGS cemented carbide substrate.