Abstract: The approximate linear model of thethree-string pendulum and its computational formula for the moment of inertiaare discussed. The influence of the excursion of the mass center of thetorsional vibrating system of the three-string pendulum on the measurement ofthe moment of inertia is analyzed. A criterion for the mass center ofthe torsional vibrating system to be in alignment with the central axis ofthe three-string pendulum and a practical method to measure the moment of inertia of a body about a noncentral axis of mass using the three-stringpendulum are proposed. It is shown that the present method is effective andreliable. Several concrete measuresfor improving precision of measuring the moment of inertia are proposed.