Two-dimensional materials have garnered widespread attention due to their unique photoelectric properties at the nanoscale, showcasing distinctive application advantages in the fields of nano-electronic devices, optics, and energy. Notably, the phonon polaritons generated by the coupled excitation of phonons and photons in two-dimensional materials exhibit highly localized at the nanometer scale, presenting substantial application potential in cutting-edge research fields such as optical manipulation and energy transmission of on-chip photonics. Infrared imaging of the sample revealed that at the sample's edge, the mutual interference of phonon polaritons resulted in the fomation of polarization standing wave fringes parallel to the edge. The fringe period effectively reflects the coupling characteristics of phonon polaritons. Therefore, the study of modulated phonon polariton coupling primarily relies on the precise measurement of the interference fringe period. The current measurement method depends on the linear fitting calculation of image analysis software, and its accuracy is constrained by the image resolution. Additionally, the displacement errors occur in the sample loading stage of SNOM. To enhance measurement accuracy and minimize the impact of the these errors on the measured value, this paper proposes the use a self-traceable chromium grating for the precise measurement of the period of the polariton interference fringe in hBN.In this paper, we present a self-traceable grating-hBN composite structure. The construction involves depositing a chromium grating on the silicon substrate using atomic lithography. The gaps between adjacent grating structures consist of air, and the two-dimensional polar material hBN is placed on the chromium grating. The dispersion of phonon polaritons generated by the recombination of hBN and different media is analyzed using Fabry-Perot quantization conditions. The study further investigates the phonon polariton coupling enhancement and modulation characteristics of two-dimensional polar materials resulting from periodic changes in metal grating structures. Scanning near-field optical microscopy (SNOM) was employed to image the phonon polaritons of the composite structure in near-field space during sample processing. Imaging of different sizes is conducted at the same point, and two methods are employed for image processing for comparison. The first method involves traditional linear fitting based on Gwyddion for calculating the interference fringe period, while the second one utilizes the use of image analysis program to perform self-traceable grating comparison measurement on the fringe period.When using the traditional Gwyddion-based linear fitting for calculating the interference fringe period, the measured fringe period in the 1 µm×1 µm near-field optical imaging is 0.264 µm, in the 5 µm×5 µm image is 0.254 µm, and in the 10 µm×10 µm image is 0.257 µm. It is observed that when the size of the measurement image is small, the error offset is large. After a large-scale scanning, the measurement value tends to stabilize, yet the overall measurement result remains unstable. Considering the 10 nm resolution of SNOM, the standard deviation value is calculated as 4 nm. Simultaneously, the image analysis program is employed to perform self-traceable grating comparison measurement on the fringe period, The grating period serves as the scale for measuring the interference fringe period. The fringe periods measured in 1 µm×1 µm, 5 µm×5 µm and 10 µm×10 µm images are 261.28 nm, 260.35 nm, 261.41 nm respectively, with a standard deviation of the measured values at 0.34 nm. Compared with the standard deviation of 4 nm from the traditional measurement method, this presents an order of magnitude reduction, achieving higher precision. When the self-traceable grating is employed, it not only measure the period size, but also calibrate the measurement point of the detection equipment. Taking SNOM in this study as an example, the calibration size ΔU of the equipment displacement device is approximately -0.18 nm/pt, with uncertainty related to the grating uncertainty, achieving sub-nanometer accuracy. However, the actual measurement still needs to consider the impact of the device resolution on measurement accuracy. By constructing a composite structure comprising a self-traceable chromium grating and a two-dimensional polar material hBN, this study leverages the periodic enhancement principle of phonon polariton intensity generated by the structural changes in the substrate grating material. Employing a scanning near-field optical microscope for imaging, the resulting composite structure exhibits coupling-enhancing fringes consistent with the self-tracing grating pitch distribution. Through image analysis and measurement, the self-traceable grating period of 212.782 nm is utilized as the scale. The interference fringe period is measured to be (261.01±0.34) nm, achieving a measurement with higher accuracy than the uncertainty of the traditional fitting method. Simultaneously, nanoscale calibration of the device can be realized based on the measurement results. In this paper, the imaging calibration of the SNOM device is determined to be -0.18 nm/pt, with uncertainty linked to the grating uncertainty. This grating metrology method offers a measurement approach with superior accuracy and reliability for precisely measuring the excitation wavelength of phonon polaritons and controlling the coupling of photon and phonon. Additionally, it provides an experimental basis for the design and regulation of two-dimensional materials applied to nanoscale devices.