Disclosed is a processing center multi-axis joint deflection loading apparatus comprising a load-receiving test piece and a load-exerting component. The load-exerting component is constituted by a steel ball, a cap, a ball socket, a bent board, a force sensor, a connection component A, and a connection component B. The connection component A is fixedly connected to a blade handle of the processing center; the blade handle is pulled tight within a bored hole on a main axle; and the connection component A is connected to a main housing via the connection component B. In a method using the apparatus for an inspection of static stiffness distribution, by means of a multi-axle joint movement, moving the load-exerting component and the load-receiving test piece to a preset loading position, allowing the normal at a load-receiving point on a load-receiving face of the load-receiving piece to be aligned with the axis of the ball socket; with the amount of shift measured by position-shift sensors fitted on the main axle, the main axle housing, and a working platform, and the amount of simulated load measured by the force sensor of the loaded-exerting component, deriving a stiffness measurement of the load-exertion position under a simulated load; changing the load-exertion position by means of a multi-axle joint movement, repeating in sequence the previous steps, thus deriving a stiffness distribution under the simulated load.