Abstract: The P110 tubing joint of φ88. 9 mm×6. 45 mmextra thickened tripped in a well. Macro observation, parameter measurement, chemical composition analysis, tensile test, metallographic examination and physical tensile test under different torques were used to analyze the tripping causes, and then finite element simulation was used to further analyze the optimal torque of the P110 tubing. The results show that the connection strength of the thread will be reduced when the smaller make-up torque was used. When the tubing string was blocked, the tubing will be affected by vibration, wall friction and other radial loads, resulted in reverse sliding of the thread, loosening and tripping. Without considering the influence of thread geometric tolerance fit, thread grease friction characteristics, thread surface coating, thread making speed and other factors, through the finite element simulation calculation, it was considered that the thread reached the best state under the calculated optimal torque (interference two turns). Considering the influence of other factors, the safety factor was 1. 25. The feasibility of this value was also verified by the actual loading and unloading tests.