Abstract: This article conducted failure analysis using a directional measuring instrument, analyzed the mechanism of crack formation at the cover plate groove, and proposed a measure for optimizing the drill collar structure. Based on the finite element analysis method, the influence of stress reduction grooves with three different widths of 120 mm, 240 mm, and 360 mm on the stress distribution at the cover plate groove and the internal thread of the drill collar was explored. The failure analysis results indicated that the crack at the cover plate groove originates from the screw hole and has typical stress corrosion characteristics. The simulation results showed that adding stress reduction grooves on the outer wall of the drill collar is a practical and effective method to improve the stress distribution of the cover plate groove and enhance the strength of the threaded connection. The improvement effect of using a 240 mm wide stress reduction groove on the Von Mises stress of the cover plate groove is the best. The maximum Von-Mises stress of the upper and lower cover plate grooves is reduced by 17.8% and 17.5% respectively compared to the original scheme. The maximum Von-Mises stress of the internal thread is reduced from 265.5 MPa to 216.18 MPa. This study is of great significance for improving the strength of drill collar threaded connections, enhancing the reliability and service life of drill collars.