Abstract: This article analyzes the failure of a certain directional drilling tool, analyzes the mechanism of crack formation, and proposes a method for optimizing the structure of API drill collars. Based on the finite element analysis model, the stress distribution of the optimized drill collar structure is analyzed, and it is verified that adding stress release structures near the male and female buckle in the threaded connection area of API drill collars is a practical and effective method to improve the strength of threaded connections. The Von-Mises stress distribution of the male and female buckles is significantly improved. The research results are of great significance for improving the strength of API drill collar threaded connections, enhancing the reliability and service life of drill collars.