Most measuring methods used now can only measure the rigid body’s six inertial parameters like the moment of inertia, the product of inertia and the centre of inertia toward to two-dimensional reference system. So a new method which can measure all the nine inertial parameters toward to three-dimensional reference system is proposed. The moment of inertia of object rotating the axis is obtained by energy decay method. Through using the translation and rotation transformation theory of product of inertia, the formula of moment of inertia including the information of product of inertia and centre of inertia is deduced. Then equations are built to solve all the parameters. Furthermore, a measuring instrument is designed based on the aerostatic bearing. Results show that this new method is available and by analyzing the experimental data, suggestions are made to improve this measuring method.