There are many methods to measure the moment of inertia of objects，such as air cushion turntable method，three wire torsion pendulum and so on．As one of the most traditional measurement methods，the three wire torsion pendulum method has the advantages of accurate measurement results，convenience and rapidity. For the measurement of the moment of inertia of the concentric steel ring with uniform mass distribution and regular geometric dimensions，firstly，the theoretical value of the moment of inertia of the steel ring is obtained throug theoretical analysis，and then the step-by-step equal precision experimental measurement is carried out．In the measurement process，the causes of the error are analyzed and minimized，and the relative error between the integral value and the experimental value is less than 0．5%．It provides a reference for the systematic study

of the moment of inertia of an object under the condition of fixed axis．