Abstract: This study investigated the types and distribution characteristics of Ni-related defect centers in 4 gem-grade HPHT synthetic yellow diamond samples through IR spectroscopy, UV-Vis spectroscopy, photoluminescence (PL) spectroscopy, and spectral mapping.The results show that the Ni-related lattice defects primarily manifest as follows: Ni_s^- center (658 nm absorption/PL peak), NE8 center (794 nm PL peak), Ni-V center (883 nm/884 nm PL peaks), and Ni-N complexes (808 nm PL group peaks). After the secondary HPHT treatment, the aggregation of substitutional nitrogen atom drive the structural transition of synthetic diamond sampels from type Ⅰb to mixed type ⅠaA—Ⅰb, and finally to type ⅠaA. Concurrently, the 658 nm absorption/PL peak, diminishes with decreasing substitutional nitrogen.The secondary HPHT treatment also destabilizes Ni-N complex, resulting in the weakening or even disappearance of the 808 nm PL group peaks, while facilitating NE8 center formation through interaction between Ni and aggregated N, thereby intensifying the 794 nm PL peak. Notably, NE8 and Ni-V centers exhibit distinct uneven distribution preferences, predominantly concentrating within 110 growth sectors, while remaining undetectable in 100 and 111 growth sectors in the HPHT synthetic yellow diamond samples.