For high-cost of shale gas exploitation, and the advantage of low cost and faster ROP for water drilling in the vertical well section. So it is necessary to carry out cuttings transport mechanism of shale gas for water drilling. Based on the basic equations of fluid mechanics and turbulence transport equations, the cuttings transport model of three-dimensional wellbore annulus is established, numerical simulation using a fully implicit coupled multigrid solver technology. The model is verified the feasibility using the experimental data. Using this model to carry out the feasibility study of cuttings transport for water drilling in horizontal well. And also study the effect law of displacement of drilling fluid, cuttings bed height, cutting diameter, the viscosity of water and rotational speed of the drill string. Result has shown that water drilling both raising speed and raising efficiency comparing air drilling and aerated mud drilling. The result shows cuttings carrying capacity is basically the same for the water drilling and mud drilling, thus the cuttings carrying capacity is feasible for the horizontal well with drilling water. The numerical result shows the sensitive parameters of the displacement of drilling fluid, cuttings bed height and particle size for affecting cuttings carrying ability of water drilling. We recommend the cuttings bed thickness should not exceed 10% of the diameter of the borehole, and cuttings particle diameter is about 5mm. According to the need of drilling using the appropriate drilling mud displacement, drilling fluid viscosity and rotational speed of the drill string. Cuttings transport mechanism of water drilling can provide technical support for safe and efficient exploitation of shale gas, and will accelerate the development process of shale gas project.