In the paper, under 5.8 GPa and 1300 ℃, the Li₃N doped diamond single crystals were synthesized in a cubic anvil high pressure and high temperature apparatus. Firstly, Fe₅₉Ni₂₅Co₁₆ alloy was used as the catalyst, high-purity Li₃N powder was used as the additive, industrial high-purity graphite powder was used as the carbon source, and the (100) crystal orientation of industrial grade diamond single crystal with good crystalline quality was used as the growth direction of diamond single crystal, the effect of Li₃N addition ratio on the growth of diamond single crystals was systematically investigated with a growth time of 20 h. The research results indicate that with the increase of Li₃N addition ratio, the color of diamond single crystals gradually transitions from yellow green, green, and dark green to dark green, and their morphology gradually transitions from hexahedron, hexahedron to octahedron. Moreover, the growth rate of single crystals decreases with the gradual increase of Li₃N addition ratio, which can be attributed to the phenomenon of upward movement in the “V-shaped region” of diamond single crystal growth with the gradual increase of Li₃N addition ratio in the P-T phase diagram of carbon. Secondly, using Fourier transform infrared (FTIR) spectroscopy, it was revealed that the nitrogen content of diamond single crystals increases with the increase of Li₃N addition ratio, and increasing the diamond growth pressure can achieve the increase in the nitrogen content of diamond single crystals. Figure 5 shows FTIR spectra of diamond crystals synthesized under different Li₃N addition ratios. When the weight percent of Li₃N added to the catalyst is 0.55%, the nitrogen content of the grown diamond single crystal is 8.92×10^–4. Thirdly, Raman spectroscopy testing revealed that the Raman characteristic peak of diamond single crystals gradually shifts towards the low-energy end with the increase of Li₃N addition ratio, which is related to the increase of internal stress in diamond single crystals. Finally, the PL spectroscopy test results showed that this study achieved high temperature and high pressure preparation of diamond single crystals with NV^– color centers, and the zero phonon line intensity of NV^– color centers in the single crystals significantly decreased with the increase of crystal nitrogen content. Figure 7 shows PL spectra of diamond crystals synthesized under different Li₃N addition ratios.