It discusses the measurement principle and the mechanical structure of 3D non-destructive measurement device for the homogeneous entity. The measurement project and its operating process is discussed. The basic operation principle and components of this measurement device are pointed out. Based on the modern design theory, optimization design, dynamical design, the mechanical structure of the device is analyzed and improved for assuring measurement precision, structural intensity, and vibration characteristic of the device. The primary experiment devices and their precision are designed and analyzed. Proved through principium experiment, the structure satisfies the request of the measuring precision. The mechanical structure of this measure device is effective and feasible.