Abstract: The rocks in deep and complex formations are commonly characterized by high hardness, strong heterogeneity, poor drillability and high abrasiveness, so low rate of penetration (ROP), short service life and high cost have always been the main technical bottlenecks that restrict the efficient application of PDC bits in deep and complex formations.Obviously, it is of great practical significance to study further the methods to improve PDC bits.The latest PDC bits and the related technologies at home and abroad were investigated, and the comprehensive PDC bit improvement method for deep and complex formations was put forward from four aspects, i.e., increasing ROP, prolonging service life, enhancing stability and optimizing steerability.Then, by virtue of this method, six PDC bits were designed to drill different types of hard formations (e.g.granite, competent sandstone and conglomerate) in Huabei and Northeast Oilfields.It is shown that these improved PDC bits are superior to conventional PDC bits and cone bits in terms of rock breaking efficiency and service life.It is indicated that this comprehensive improvement method has good applicability and use value.The research results provide the theoretical and practical guidance for the optimal design of PDC bits in deep and complicated formations.