Diamonds are very rare in nature and are hence extremely precious mineral resources. The diamond of metamorphic origin, discovered in several ultrahigh pressures metamorphic zones in the world, has improved our understanding of ultrahigh pressure metamorphism and plate tectonic movement. Moreover, it has promoted the research on geodynamics of ultrahigh pressure metamorphic belt and attracted extensive attentions. However, further discussion is needed on the formation mechanism of metamorphic diamond. Based on recent research results, the authors described the tectonic background for the formation of metamorphic diamond, studied the geological environment and temperature-pressure conditions and discussed the origin of the diamond in the ultrahigh-pressure metamorphic zone. When the peak pressure of metamorphism reaches the stable region of diamond and has a higher temperature (pressure>3 GPa, temperature 600℃~1 000℃), the conditions are beneficial to the formation of diamond. Higher CO₂ content and lower oxygen fugacity in C-O-H fluids are also essential for diamond formation in ultrahigh pressure metamorphic belts. In addition, the cooling effect at the early exhumation is favorable for its preservation.