The accurate measurement and control of center of mass (CM) in mass properties for satellite attitude control are the most important. In order to accurately measure CM, this paper describes a new type of CM measuring instruments which are particularly recommended for determining mass properties of rockets, satellite and ballistic objects. A spherical air-bearing supports a precision rotary table and acts as a frictionless pivot axis for measuring unbalance moments due to the displacement of the test part CM relative to the central axis of the bearing. This paper emphasizes the research on reasons and laws of the load table CM offset caused by the elastic deformation, and according to curve theory of thin plates derives the formulary for the element center of mass displacement of the finite element and for the platform structure center of mass elastic displacement, and calculates the CM elasticity offset and the unbalance moment caused by the deformation of loaded table. The research results provide bases for the structure design of rotary tables.