In this work, we presented the influence of catalyst geometric construction on temperature distribution, flow structure, the transport processes of the carbon atoms, and the resulting diamond growth in the process of HPHT diamond synthesis. Several catalyst geometry models were tested, and the experimental results of growth rates were compared with numerical simulations. We revealed that increasing the protrusion diameter of the convex-shaped catalysts could significantly improve the growth rate of diamonds. The diamond growth rate was improved from 1.6 mg h -1 to 4 mg h -1 when the protrusion diameter was enlarged by 2 mm. These results will be discussed through the characteristic distributions of the temperature and convection fields in the process of diamond growth.