During drilling of clay layer, accidents such as shrinkage, collapse, adhesion and drilling are prone to occur, as well as mud-packing drill bits and pumping; and the clay soil layer has a certain slurry-making ability, which changes the performance indicators of the drilling fluid; at the same time, the drilling fluid directly erodes the core, affecting the drilling efficiency and the quality of the core. By conducting in-depth analysis of the mechanical properties, hydration mechanism, the influence of flushing fluid, and core protection of the clay, we then adopt methods for drilling bits and cores, and optimize the drilling process through design improvement, experimental analysis, and on-site practice, improving the drilling efficiency in the clay layer and reducing the drilling cost of bottoming.