Extended reach wells have been widely used in oil and gas reservoir exploitation in deep formations. However, a series of downhole problems, such as inefficient hole cleaning, back pressure, and pipe sticking, are also encountered. To better guide hole cleaning, the dynamic characteristics of cuttings transport in long open hole section of ultra-deep extended reach wells must be studied further. According to the law of mass conservation and the momentum theorem, a two-layer dynamic cuttings transport model of extend reach wells is established, considering the actual hole trajectory, fluid pressure drop, and particle diffusion in the suspension layer. The model is solved by the finite difference method and verified by the experimental results in the existing literature. This study simulates the process of drilling and well washing and analyzes the influence of the drilling fluid flow rates, the drilling fluid density, the rate of penetration (ROP), and the wellbore diameter on cuttings transport. Research results demonstrate that, under drilling conditions, cuttings are difficult to deposit in the section with a small inclination angle, the degree of hole cleaning increases with the flow rates and the drilling fluid density, and the smaller wellbore diameter is, the lower the ROP is, which is helpful in hole cleaning. Under well washing conditions, the smaller the inclination angle of the well is, the worse the erosion effect is, and the smaller wellbore diameter is, the higher the efficiency of cuttings transport is; the degree of hole cleaning increases with the flow rates and the drilling fluid density. The research results have a guiding significance for ensuring the good hole cleaning of ultra-deep extended reach wells.