Localization of photons holds significant implications in both fundamental research and technological applications. Bound states in the continuum (BICs) in photonic crystal provide a novel mechanism for effective photon localization. However, fabrication imperfections and defects are inevitable during the manufacturing process of photonic crystals. Momentum-space characterization serves as a powerful tool to analyze how such processing variations affect the photonic band structure, thereby informing the design and fabrication of photonic crystal devices. This paper designs a photonic crystal in the visible light band and analyzes its band structure through FDTD simulation. The high symmetry at the momentum space Γ point leads to a symmetry mismatch between the internal mode of the photonic crystal and the external propagation mode (radiation continuum), so that bound states with infinite lifetime appear above the light, realizing localization in the vertical direction. At the same time, this paper measures the angle-resolved photoluminescence (PL) spectrum of the photonic crystal through the self-built angle-resolved optical path. The weak photoluminescence of the Si₃N₄ substrate is coupled with the photonic crystal mode to measure the photonic crystal band. It can be observed that the band structure is consistent with the simulation results. At the same time, the intensity of the TE₁ band near the Γ point is significantly weakened compared to the intensity at the position away from the Γ point, but it is not completely eliminated. This shows that processing errors and defects will destroy the symmetry of the structure, causing the BIC to evolve into the quasi-BIC. The quasi-BIC mode achieves effective localization of photons in the vertical direction near the Γ point. Furthermore, a heterostructure of different periodic photonic crystals was designed to attain lateral photon localization by utilizing the band nesting of the two. In this way, this study culminated in the development of high-quality microcavities with an impressive quality factor to mode volume ratio of 6×10¹⁴ cm^-3, and achieved characteristic regulation of the momentum space of the photonic crystal by adjusting the structural parameters. This research is of great significant for the design of photonic crystals and the interaction between light and matter.