Abstract: The reform project of a test bench is mainly used for the test of main reducing tension bearing，and the test instrument is equipped with the function of applying load and speed. During the trial，the traditional single closedloop control can not meet the test requirements. In order to complete the experiment content，control mode was improved in the program debugging，self-tuning PID controller was used to calculate the PI parameters，single closedloop control and double closed-loop control method were used flexibly，and on the basis of the double closed-loop control，the improvement of linear input was added，the system dynamic response characteristics were promoted，and the control of system tension，bending moment，lateral force were completed at last. The experimental results show that compared with the single closed-loop control system，the double closed-loop control system has better dynamic and static performance，meets the test requirements more.

      Key words: PID control；double closed-loop；tension bearing test；force value control