Abstract: It is one of the important requisites in the engine mounting system design to accurately determine the inertia properties of a powertrain rigid body. Observing that trifilar torsional pendulum can precisely measure mass moment of inertia of complex rigid body, an experimental methodology for inertia parameter identification is proposed, in which the rigid body is positioned at 6~9 different orientations represented with three-points on the rigid body. The key points include: (1) the orientation of the rigid body is indirectly determined with three points on the rigid body, and a movable coordinate system is defined with the normal vector of plane formed by the three on-body points; (2) distances between the three on-body points and reference points on the pendulum plate (defining a global coordinate system) are measured for each test, and global coordinates of the three on-body points and the coordinate transformation between the two coordinate frames are determined；(3) the rotation axis orientation of the rigid body and the moment of inertia for each test under the movable coordinates are calculated; and (4) utilizing least square principle, the optimal intersection “point” of the rotation axis of each test is determined to be the center of gravity, and then a set of linear equations derived from the transformation formula of rigid-body moment of inertia about different axis rotation is solved to identify inertia tensor of the rigid body. Some factors that may produce errors still exist in the proposed identification procedure, but they can be estimated and effectively reduced at every step with least square method. The practicability and reliability of the procedure is illustrated by error analysis, validation of cuboid mass block and many tests of real powertrains.