The interesting relationship between the genesis of synthetic and natural diamonds can be got according to the studies of synthetic diamonds and rapid development of diamond industry. However there are still active argument about genesis of natural diamond among in the geoscientific workers.On the basis of research of synthetic diamonds, we pointed out that carbon source, catalysts (ore catalysts), temperature and pressure of systems are very important and significant natural condition for producing diamonds. In this paper it has been shown that the calcium carbonate or other carbonates have a close relation to the natural diamond. The former can be regarded as a kind of carbon source for the latter.-The authors of this paper have made experiments by using calcium carbonate as a carbon source for synthesizing diamond some diamond crystals have been recognized by scattering electronic microscope in size up to 7-9 micron. The samples studied at different temperature and pressure are also masured by X-ray diffraction. These experimental results show a good symbol for researching genesis of natural diamonds, consequently our study concerned that is changed correspondingly from pure theoretical to practical character, from indirect approach to direct experiments.