Diamond films was deposited on cemented carbide tools with two-step pretreatment method under different distances between the substrates and hot filaments, and the effect of the distance between the substrates and hot filaments on the crystallographic orientation of diamond films and the characteristics of diamond coated tools was investigated in bias-enhanced HFCVD system in this paper. The cutting performance of diamond coated tools was verified by the experiments of cutting particles reinforced aluminum base composite material with 15 vol.% Si as compared with uncoated ones. The quality of diamond film was analyzed by means of Scanning Electron Microscopy(SEM), Raman spectroscopy, and X-ray diffraction. The optimization deposition processing was obtained. The relative intensity ratio of (111) facet and (220) facet in the film tested by XRD was one third. The cutting performance of diamond coated tool was improved significantly when machining the Si particle reinforced aluminum-based metal matrix composite; its lifetime was 30 times longer than that of uncoated one. The work done in this paper was of great practical significance to accelerate the industrialization of diamond films coated WC–Co substrates.