By utilizing the parallel axis theorem of moment of inertia and the graphic geometric transformation theory as well as the method of rotating and moving axis, the calculation formula of irregular objects’ centroid was derived. And on the basis of a single axis air bearing table which was used for measuring the moment of inertia of objects around a fixed axis, the complete instrument of measuring the irregular objects’ centroid was designed. The objects’ centroid and moment of inertia could be measured synchronously. Through the analysis of the influence on measuring accuracy caused by measuring factors’ errors, the method of improving the measuring accuracy of instrument was derived. The measuring instrument meets the requirement of measuring the irregular objects’ centroid precisely.