On this paper, diamond coatings with completely different microstructure have been ready on cemented carbide substrates by HFCVD method. The adjustments of grain development mode and dimension of diamond coating underneath completely different substrate temperature (800 °C, 850 °C, 900 °C) and carbon supply focus (2%, 4%, 6%) have been studied, and the variations of coating efficiency have been explored. Each substrate temperature and carbon supply focus impact grain dimension. When the grain dimension is in micron scale (0.5 ∼ 6 μm), the expansion mode is columnar crystal competing development. When the substrate temperature reaches 900 °C and the carbon supply focus is 6%, the diamond grain can be absolutely secondary nucleated, and the grain dimension will scale back to the nanometer scale (20 ∼ 50 nm). The expansion mode is particle cluster accumulation development and the speed of development will increase considerably. The rise of grain dimension will improve the adhesion of the coating and its resistance to put on and exterior loading. Nonetheless, it could result in bigger friction coefficient, which is about 0.1. As a result of small grain dimension, the adhesion pressure of nanocrystalline diamond coating is clearly smaller than micrystalline diamond coating, however the friction coefficient is simply 0.03.