Abstract: A method of measuring torque of gear ring of torque multiplier is presented to realize dynamic real-time monitoring of pre-tightening torque of bolt. The stiffness and strength of the bellows are simulated by ANSYS, and the influence of angle, temperature and friction loss of the torque multiplier on the measurement sensitivity is considered. On this basis, the test platform of bolt torque monitoring device is built and verified by downhole test. The results show that the friction loss of torque multiplier leads to the measurement error of no more than 6.2%. The linear relationship between measuring torque and bellows pressure is maintained. The monitoring device can realize real-time and effective control of bolt torque.