The optical axis dynamic range and detection sensitivity are limited by the focal length of the image lens. The focus gets used to be lengthened for enhancing the detection sensitivity, but the dynamic range will become narrow. In this paper, we proposed a new optical path structure on the basis of a two-dimension orthogonal diffraction grating. A corresponding experimental setup was built to compare the dynamic range and centroid detection accuracy of the new method and the conventional method under the same experiment conditions. The experimental results show that the optical axis dynamic range is enlarged obviously, and the high-precision centroid is detected at the same time.