Abstract: The constant torque method is one of the most widely used methods in the industry at present. The accurate torque value is an indispensable element to ensure the effective connection, and it is also the basis of production operation. Based on the preset mode of the thread on the connected workpiece, this paper divides it into five models: no thread, self set internal thread, built-in internal thread, external internal thread and external external external thread. After analyzing the failure modes of five connecting body models, the factors of torque value are deduced in reverse direction. The factors in different forms are divided into six stages to determine. By calculating the failure torque, determining the value object and verifying the reliability of the torque, the execution torque of the connecting body is obtained. At the same time, it shows that under the safe load, the larger the torque value is, the higher the material utilization rate is, the higher the reliability of the threaded connection is, and the value of the torque must protect the lowest allowable torque of the connector from being damaged.