In order to reduce the difficulty of cuttings migration in horizontal wells, the problem of bit bagging. Improve the drilling efficiency and service life of PDC drill bit in the process of shale horizontal well drilling. The numerical simulation method and the low Reynolds number k-ԑ turbulence model are used to establish the bottom hole flow field model. The hydraulic structure of the PDC (polycrystalline diamond compact) bit is analyzed under the conditions of different drilling fluid displacement, PDC bit rotation speed and cuttings particle size. The results show that: with the increase of displacement, cuttings efficiency increases gradually. However, in the rotating condition, the mismatch between the drilling fluid displacement and the drill bit speed reduces the drilling fluid scour and cuttings migration efficiency. Appropriate displacement and rotational speed can effectively improve the cuttings migration efficiency and reduce the accumulation of cuttings at the bottom of the well. Under a certain bit rotation speed and drilling fluid displacement, the particle size of cuttings is directly proportional to the cuttings migration efficiency. The research results can provide reference for optimizing the design of PDC bit and drilling construction parameters.