Polycrystalline diamond compacts (PDCs) are extensively utilized in petroleum drilling, geological exploration, and high-performance machining tools. Notably, gradient structure has demonstrated significant efficacy in reducing interfacial residual stresses within PDCs, thereby enhancing the mechanical performance. However, investigation into the effect of gradient parameters on the microstructure and performance of PDCs has rarely been investigated in practice. This study utilized material extrusion 3D printing technology to manufacture gradient PDCs with different gradient layer thickness. Transition in microstructure and element distribution inside gradient layers were characterized with scanning electron microscopy and energy-dispersive spectroscopy. Subsequently, wear resistant and impact toughness of gradient PDCs and conventional PDC were systematically investigated via vertical turret lathe and drop-weight impact test. All gradient PDCs exhibited a counter-gradient distribution of diamond and tungsten carbide within their gradient layers, but the compositional gradient evolution rate progressively decreased with the increase of gradient layer thickness. Inhomogeneous cobalt diffusion induced the formation of Co-depleted zones with their spatial extent expanding progressively with increasing gradient layer thickness. WC grains in the gradient layer exhibited progressive homogeneous refinement from the cemented carbide substrate toward the PCD layer, which is closely related to the cobalt distribution. The gradient PDC including 8 gradient sublayers with a thickness of 0.1 mm per layer demonstrated a 12.3 % enhancement in impact resistance and 22.7 % improvement in wear resistance compared to conventional PDC. The study results can provide valuable insights and guidance for the design of gradient structure for high-quality PDCs.