Abstract: In this paper, the effects of initial diamond particle sizes on the mechanical properties of PDC (Polycrystalline Diamond Compact) cutters for oil and gas drilling were systematically investigated. The microscopic features of eight single-grain-size diamond powders were analyzed. The microstructures of the PDC cutters prepared from different grain sizes of diamond powders were characterized. The mechanical properties of coarse-grained PDC including hardness, fracture toughness, abrasion resistance, impact toughness and thermal stability were tested. Cold compaction experiments were performed on diamond powders with different single and double grain size formulations. Three kinds of double-grain-size formulations were determined through the analysis of a large number of tests on the vertical turning lathe (VTL) rock-cutting performance of PDC cutters. The double-layer structured PDC cutters were designed, with fine-grained diamond as the upper layer and coarse-grained diamond as the lower layer to achieve balanced wear-resistance and impact resistance. On the basis of the three double-particle-size formulations, combined with the influence of different filler particle ratios on the performance of PDCs with different main grain size systems, the trimodal particle size formulations were further designed. The optimal formulations with three different performance orientations were obtained under the experimental system of the present study, i.e. wear-resistant formulation, impact resistant formulation and balanced formulation.