Abstract: The magnetism of zigzag graphene nanoribbon (ZZ-GNR) represents a pivotal topic in carbon-based spintronics. Recently, our research team experimentally verified the presence of intrinsic magnetism in ZZ-GNR by embedding them within a hexagonal boron nitride (hBN) lattice. However, prior scanning nitrogen-vacancy microscopy (SNVM) measurements only captured the magnetic field's projected component along the nitrogen-vacancy center axis, complicating the direct visualization of magnetic anisotropy characteristics through imaging. Building upon our previous findings, this paper introduces a magnetic field vector reconstruction method based on Fourier transform. By applying the constraints of Maxwell's equations in current-free regions, we successfully reconstructed the three-dimensional vector stray magnetic fields (B_x, B_y, B_z) of ZZ-GNR from the original Full-B mode data. Quantitative analysis reveals that the stray magnetic field generated by the ZZ-GNR edges is predominantly oriented in the out-of-plane direction (B_z), with a peak intensity of approximately 0.37 mT, while the in-plane components are minimal. Supported by control experiments on armchair graphene nanoribbons (AC-GNR) and empty trenches, this study provides direct confirmation of the pronounced perpendicular magnetic anisotropy of embedded ZZ-GNR at the nanoscale, offering crucial quantitative experimental evidence for understanding their ferrimagnetic ground state.