Drilling tools are important instruments in oilfield drilling construction, the qualities of which determine the progress of oilfield drilling to some extent. With the deepening development of oilfield, the working conditions of drilling tools are becoming more and more complicated and severe, and the failure accidents happen rather often at present stage. In the directional drilling project of an oilfield block, wear and corrosion of some drilling tools were found. By analyzing the microstructure, element composition and corrosion products of the failed drilling tools, it was found that Cl− in the solution and Al2O3 in the drilling mud were the main causes of the corrosion and wear failure of the drilling tools. The Cl− passed through the CrxOy passivation film and caused pitting pits inside the drilling tools. The pitting pits continued to grow, expand and merge as the corrosion progressing, thus forming a large area of pitting pits on the surface of the failed drilling tools. In addition, Al2O3 particles in the drilling mud would destroy the TiN coating under high-speed fluid erosion, leading to the exposure of the stainless steel substrate. Therefore, it was difficult to form a dense and stable passivation film at the damaged location under the severe conditions of high temperature, high pressure and high-speed fluid, thus resulting in a porous structure of the passivation film. The porous passivation film cannot prevent corrosion effectively. On the contrary, the coating and the steel matrix would form corrosion galvanic cells, further intensifying the corrosion extent of the drilling tools. In the end, the preventive measures were put forward to reduce the failure accidents of the drilling tools, which has guiding significance for scientific use of drilling tools in oilfield.