Abstract: With oil and gas exploration advancing towards deep, ultra-deep, and extra-deep reservoirs, complex geological environments have imposed stringent demands on drilling tools. This paper systematically reviews the rock-breaking mechanisms, failure modes, material and structural optimization, and the current status of intelligent development of Polycrystalline Diamond Compact (PDC) bits in deep complex formations, providing theoretical support and engineering references for high-efficiency bit design. By summarizing single-cutter experiments, numerical simulations, microstructural analyses, and field data studies, this paper analyzes plastic-brittle failure patterns of rocks under various formation conditions and their effects on cutting forces, mechanical specific energy (MSE), and cutting morphology. It systematically categorizes typical failure modes of PDC cutters, including wear, impact, and erosion. Furthermore, it evaluates recent progress in cutter material modification, shaped cutter design, global cutter layout, and hydraulic structure optimization technologies regarding their roles in enhancing rock-breaking efficiency and bit lifespan. The paper also outlines the research and application of smart bits and machine learning-based bit selection methods in deep drilling operations. Material and structural optimization can enhance the adaptability of PDC bits in deep oil and gas drilling, while intelligent technologies provide effective support for bit selection, lifespan prediction, and operational safety. The future development trend of PDC bit technology should focus on the deep synergy of materials, structures, and intelligence to achieve efficient rock breaking and optimize drilling operations in deep and complex formations.