Terahertz dual-axis reflection confocal scanning imaging technique can penetrate nonpolar and non-metallic materials and then realizes high-resolution 3D imaging, thus it has wide research and application values. Its 2D imaging quality is greatly related to the axial position of the object. Experiments about the influence of the object axial position on the 2D imaging quality are carried out by utilizing 2.52 THz dual-axis reflection confocal scanning imaging system. Line contrast and area contrast are introduced to objectively evaluate the imaging quality. The subjective evaluation tallies with the objective evaluation basically.