A design method for a personalized drill bit for a complex difficult-to-drill formation includes: S1, acquiring rock drillability indexes of a drilled formation; S2, performing digital simulation analysis of rock breaking of bit teeth and a composite rock breaking experiment of a ring gear and a drill bit, and establishing a mechanical model of the rock interaction at the bottom of a well; S3, establishing an integrated dynamics model of drill string-drill bit-rock system coupling; S4, designing a tooth shape, a tooth distribution density, a crown shape and a gauge protection structure for rock mechanics properties of a complex difficult-to-drill formation; S5, optimizing bit nozzle and hydraulic structure parameters by using the computational fluid dynamics theory and the numerical simulation method; S6. optimizing a manufacturing process of the drill bit by using the tooth material decarburization strengthening technology, the high-strength bit body material technology and the special tooth-shaped tooth technology.