Diamond coated hard metal is an outstanding cutting material for manufacturing. By adding SiC to the diamond coating material, not only the surface toughness but also the film adhesive strength can be improved. Diamond/β-SiC/cobalt silicide composite films were deposited on Co-cemented tungsten carbide (WC-Co) substrates by direct current plasma assisted hot filament chemical vapor deposition using a gas mixture of hydrogen, methane and tetramethylsilane. Scanning electron microscopy, electron probe microanalysis, X-ray diffraction and Raman scattering analyses were carried out to characterize the surface morphology, composition and structure of the deposited films. The results revealed that the composite films consist of diamond, β-SiC and cobalt silicides (Co2Si, CoSi). The structure and composition of the composite films can be controlled by adjusting bias current and tetramethylsilane concentration in the gas phase. With the increase of bias current, the grain size and content of diamond also increase, while the content of β-SiC decrease. Since bias current enhances the secondary nucleation and growth of diamond. Although the dissociation of hydrogen, methane and tetramethylsilane are all enhanced by electron bombardment during the biasing process, the concentration of produced C sources is much higher than that of Si sources with the increase of bias current. Then the growth of diamond becomes more competitive than that of β-SiC. The bias current cannot be too high to deposit the three substances of diamond, β-SiC and cobalt silicides. By adjusting bias and gas composition, the distribution of diamond and β-SiC in the composite films was manipulated. These results demonstrated the significance to understand and control the growth of composite materials and super hard thin films. Such composite films can be utilized to improve the cutting performance of diamond coated cutting tools.