The invention discloses a center torsion bar type object mass center and rotational inertia measuring mechanism based on knife edge support. A problem is solved by a method of giving two functions through a center shaft, and the shaft is a reference shaft system for measuring the mass center rotation, and a swing torsion bar used for measuring the rotational inertia. According to the mechanism, atraditional design concept is broken through in the three aspects, firstly, the rigidity of the torsion bar should not be too large, otherwise an initial angle with a certain value is difficult to twist, and when the swing angle is large, the swing is stable, and the periodic measurement is facilitated; secondly, the rigidity is too large, the swing frequency is fast, and the swing period is difficult to measure; and thirdly, the rigidity of a rotating shaft for measuring the mass center should be large, a corner of the shaft system cannot be caused by a driving friction moment, and otherwisethe rotating shaft cannot stop immediately when the rotation is stopped and can swing in a reciprocating mode.